foo.cc: In function ‘int main()’:
foo.cc:6:12: error: no match for ‘operator<<’ (operand types are ‘std::istream’ {aka ‘std::basic_istream<char>’} and ‘int’)
    6 |         cin<<a;
      |         ~~~^~~
      |         |    |
      |         |    int
      |         std::istream {aka std::basic_istream<char>}
foo.cc:6:12: note: candidate: ‘operator<<(int, int)’ (built-in)
    6 |         cin<<a;
      |         ~~~^~~
foo.cc:6:12: note:   no known conversion for argument 1 from ‘std::istream’ {aka ‘std::basic_istream<char>’} to ‘int’
In file included from /nix/gcc-13.2.0/include/c++/13.2.0/regex:68,
                 from stdc++.h:181:
/nix/gcc-13.2.0/include/c++/13.2.0/bits/regex.h:1715:5: note: candidate: ‘template<class _Ch_type, class _Ch_traits, class _Bi_iter> std::basic_ostream<_CharT, _Traits>& std::__cxx11::operator<<(std::basic_ostream<_CharT, _Traits>&, const sub_match<_Bi_iter>&)’
 1715 |     operator<<(basic_ostream<_Ch_type, _Ch_traits>& __os,
      |     ^~~~~~~~
/nix/gcc-13.2.0/include/c++/13.2.0/bits/regex.h:1715:5: note:   template argument deduction/substitution failed:
foo.cc:6:14: note:   ‘std::istream’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |         cin<<a;
      |              ^
In file included from /nix/gcc-13.2.0/include/c++/13.2.0/string:54,
                 from /nix/gcc-13.2.0/include/c++/13.2.0/bitset:52,
                 from stdc++.h:52:
/nix/gcc-13.2.0/include/c++/13.2.0/bits/basic_string.h:4020:5: note: candidate: ‘template<class _CharT, class _Traits, class _Alloc> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, const __cxx11::basic_string<_CharT, _Traits, _Alloc>&)’
 4020 |     operator<<(basic_ostream<_CharT, _Traits>& __os,
      |     ^~~~~~~~
/nix/gcc-13.2.0/include/c++/13.2.0/bits/basic_string.h:4020:5: note:   template argument deduction/substitution failed:
foo.cc:6:14: note:   ‘std::istream’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |         cin<<a;
      |              ^
/nix/gcc-13.2.0/include/c++/13.2.0/bitset:1683:5: note: candidate: ‘template<class _CharT, class _Traits, long unsigned int _Nb> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, const bitset<_Nb>&)’
 1683 |     operator<<(std::basic_ostream<_CharT, _Traits>& __os,
      |     ^~~~~~~~
/nix/gcc-13.2.0/include/c++/13.2.0/bitset:1683:5: note:   template argument deduction/substitution failed:
foo.cc:6:14: note:   ‘std::istream’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |         cin<<a;
      |              ^
In file included from /nix/gcc-13.2.0/include/c++/13.2.0/bits/ios_base.h:46,
                 from /nix/gcc-13.2.0/include/c++/13.2.0/streambuf:43,
                 from /nix/gcc-13.2.0/include/c++/13.2.0/bits/streambuf_iterator.h:35,
                 from /nix/gcc-13.2.0/include/c++/13.2.0/iterator:66,
                 from stdc++.h:54:
/nix/gcc-13.2.0/include/c++/13.2.0/system_error:339:5: note: candidate: ‘template<class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, const error_code&)’
  339 |     operator<<(basic_ostream<_CharT, _Traits>& __os, const error_code& __e)
      |     ^~~~~~~~
/nix/gcc-13.2.0/include/c++/13.2.0/system_error:339:5: note:   template argument deduction/substitution failed:
foo.cc:6:14: note:   ‘std::istream’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |         cin<<a;
      |              ^
In file included from /nix/gcc-13.2.0/include/c++/13.2.0/memory:80,
                 from stdc++.h:56:
/nix/gcc-13.2.0/include/c++/13.2.0/bits/shared_ptr.h:70:5: note: candidate: ‘template<class _Ch, class _Tr, class _Tp, __gnu_cxx::_Lock_policy _Lp> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, const __shared_ptr<_Tp, _Lp>&)’
   70 |     operator<<(std::basic_ostream<_Ch, _Tr>& __os,
      |     ^~~~~~~~
/nix/gcc-13.2.0/include/c++/13.2.0/bits/shared_ptr.h:70:5: note:   template argument deduction/substitution failed:
foo.cc:6:14: note:   ‘std::istream’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |         cin<<a;
      |              ^
In file included from /nix/gcc-13.2.0/include/c++/13.2.0/istream:41,
                 from /nix/gcc-13.2.0/include/c++/13.2.0/sstream:40,
                 from /nix/gcc-13.2.0/include/c++/13.2.0/complex:45,
                 from /nix/gcc-13.2.0/include/c++/13.2.0/ccomplex:39,
                 from stdc++.h:127:
/nix/gcc-13.2.0/include/c++/13.2.0/ostream:554:5: note: candidate: ‘template<class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, _CharT)’
  554 |     operator<<(basic_ostream<_CharT, _Traits>& __out, _CharT __c)
      |     ^~~~~~~~
/nix/gcc-13.2.0/include/c++/13.2.0/ostream:554:5: note:   template argument deduction/substitution failed:
foo.cc:6:14: note:   ‘std::istream’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |         cin<<a;
      |              ^
/nix/gcc-13.2.0/include/c++/13.2.0/ostream:564:5: note: candidate: ‘template<class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, char)’
  564 |     operator<<(basic_ostream<_CharT, _Traits>& __out, char __c)
      |     ^~~~~~~~
/nix/gcc-13.2.0/include/c++/13.2.0/ostream:564:5: note:   template argument deduction/substitution failed:
foo.cc:6:14: note:   ‘std::istream’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |         cin<<a;
      |              ^
/nix/gcc-13.2.0/include/c++/13.2.0/ostream:570:5: note: candidate: ‘template<class _Traits> std::basic_ostream<char, _Traits>& std::operator<<(basic_ostream<char, _Traits>&, char)’
  570 |     operator<<(basic_ostream<char, _Traits>& __out, char __c)
      |     ^~~~~~~~
/nix/gcc-13.2.0/include/c++/13.2.0/ostream:570:5: note:   template argument deduction/substitution failed:
foo.cc:6:14: note:   ‘std::istream’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<char, _Traits>’
    6 |         cin<<a;
      |              ^
/nix/gcc-13.2.0/include/c++/13.2.0/ostream:581:5: note: candidate: ‘template<class _Traits> std::basic_ostream<char, _Traits>& std::operator<<(basic_ostream<char, _Traits>&, signed char)’
  581 |     operator<<(basic_ostream<char, _Traits>& __out, signed char __c)
      |     ^~~~~~~~
/nix/gcc-13.2.0/include/c++/13.2.0/ostream:581:5: note:   template argument deduction/substitution failed:
foo.cc:6:14: note:   ‘std::istream’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<char, _Traits>’
    6 |         cin<<a;
      |              ^
/nix/gcc-13.2.0/include/c++/13.2.0/ostream:586:5: note: candidate: ‘template<class _Traits> std::basic_ostream<char, _Traits>& std::operator<<(basic_ostream<char, _Traits>&, unsigned char)’
  586 |     operator<<(basic_ostream<char, _Traits>& __out, unsigned char __c)
      |     ^~~~~~~~
/nix/gcc-13.2.0/include/c++/13.2.0/ostream:586:5: note:   template argument deduction/substitution failed:
foo.cc:6:14: note:   ‘std::istream’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<char, _Traits>’
    6 |         cin<<a;
      |              ^
/nix/gcc-13.2.0/include/c++/13.2.0/ostream:645:5: note: candidate: ‘template<class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, const _CharT*)’
  645 |     operator<<(basic_ostream<_CharT, _Traits>& __out, const _CharT* __s)
      |     ^~~~~~~~
/nix/gcc-13.2.0/include/c++/13.2.0/ostream:645:5: note:   template argument deduction/substitution failed:
foo.cc:6:14: note:   ‘std::istream’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |         cin<<a;
      |              ^
In file included from /nix/gcc-13.2.0/include/c++/13.2.0/ostream:880:
/nix/gcc-13.2.0/include/c++/13.2.0/bits/ostream.tcc:307:5: note: candidate: ‘template<class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, const char*)’
  307 |     operator<<(basic_ostream<_CharT, _Traits>& __out, const char* __s)
      |     ^~~~~~~~
/nix/gcc-13.2.0/include/c++/13.2.0/bits/ostream.tcc:307:5: note:   template argument deduction/substitution failed:
foo.cc:6:14: note:   ‘std::istream’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |         cin<<a;
      |              ^
/nix/gcc-13.2.0/include/c++/13.2.0/ostream:662:5: note: candidate: ‘template<class _Traits> std::basic_ostream<char, _Traits>& std::operator<<(basic_ostream<char, _Traits>&, const char*)’
  662 |     operator<<(basic_ostream<char, _Traits>& __out, const char* __s)
      |     ^~~~~~~~
/nix/gcc-13.2.0/include/c++/13.2.0/ostream:662:5: note:   template argument deduction/substitution failed:
foo.cc:6:14: note:   ‘std::istream’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<char, _Traits>’
    6 |         cin<<a;
      |              ^
/nix/gcc-13.2.0/include/c++/13.2.0/ostream:675:5: note: candidate: ‘template<class _Traits> std::basic_ostream<char, _Traits>& std::operator<<(basic_ostream<char, _Traits>&, const signed char*)’
  675 |     operator<<(basic_ostream<char, _Traits>& __out, const signed char* __s)
      |     ^~~~~~~~
/nix/gcc-13.2.0/include/c++/13.2.0/ostream:675:5: note:   template argument deduction/substitution failed:
foo.cc:6:14: note:   ‘std::istream’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<char, _Traits>’
    6 |         cin<<a;
      |              ^
/nix/gcc-13.2.0/include/c++/13.2.0/ostream:680:5: note: candidate: ‘template<class _Traits> std::basic_ostream<char, _Traits>& std::operator<<(basic_ostream<char, _Traits>&, const unsigned char*)’
  680 |     operator<<(basic_ostream<char, _Traits>& __out, const unsigned char* __s)
      |     ^~~~~~~~
/nix/gcc-13.2.0/include/c++/13.2.0/ostream:680:5: note:   template argument deduction/substitution failed:
foo.cc:6:14: note:   ‘std::istream’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<char, _Traits>’
    6 |         cin<<a;
      |              ^
/nix/gcc-13.2.0/include/c++/13.2.0/ostream:801:5: note: candidate: ‘template<class _Ostream, class _Tp> _Ostream&& std::operator<<(_Ostream&&, const _Tp&)’
  801 |     operator<<(_Ostream&& __os, const _Tp& __x)
      |     ^~~~~~~~
/nix/gcc-13.2.0/include/c++/13.2.0/ostream:801:5: note:   template argument deduction/substitution failed:
/nix/gcc-13.2.0/include/c++/13.2.0/ostream: In substitution of ‘template<class _Ostream, class _Tp> _Ostream&& std::operator<<(_Ostream&&, const _Tp&) [with _Ostream = std::basic_istream<char>&; _Tp = int]’:
foo.cc:6:7:   required from here
/nix/gcc-13.2.0/include/c++/13.2.0/ostream:801:5: error: no type named ‘type’ in ‘struct std::enable_if<false, void>’
/nix/gcc-13.2.0/include/c++/13.2.0/complex:558:5: note: candidate: ‘template<class _Tp, class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, const complex<_Tp>&)’
  558 |     operator<<(basic_ostream<_CharT, _Traits>& __os, const complex<_Tp>& __x)
      |     ^~~~~~~~
/nix/gcc-13.2.0/include/c++/13.2.0/complex:558:5: note:   template argument deduction/substitution failed:
foo.cc:6:14: note:   ‘std::istream’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |         cin<<a;
      |              ^
In file included from stdc++.h:143:
/nix/gcc-13.2.0/include/c++/13.2.0/iomanip:81:5: note: candidate: ‘template<class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, _Resetiosflags)’
   81 |     operator<<(basic_ostream<_CharT, _Traits>& __os, _Resetiosflags __f)
      |     ^~~~~~~~
/nix/gcc-13.2.0/include/c++/13.2.0/iomanip:81:5: note:   template argument deduction/substitution failed:
foo.cc:6:14: note:   ‘std::istream’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |         cin<<a;
      |              ^
/nix/gcc-13.2.0/include/c++/13.2.0/iomanip:111:5: note: candidate: ‘template<class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, _Setiosflags)’
  111 |     operator<<(basic_ostream<_CharT, _Traits>& __os, _Setiosflags __f)
      |     ^~~~~~~~
/nix/gcc-13.2.0/include/c++/13.2.0/iomanip:111:5: note:   template argument deduction/substitution failed:
foo.cc:6:14: note:   ‘std::istream’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |         cin<<a;
      |              ^
/nix/gcc-13.2.0/include/c++/13.2.0/iomanip:145:5: note: candidate: ‘template<class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, _Setbase)’
  145 |     operator<<(basic_ostream<_CharT, _Traits>& __os, _Setbase __f)
      |     ^~~~~~~~
/nix/gcc-13.2.0/include/c++/13.2.0/iomanip:145:5: note:   template argument deduction/substitution failed:
foo.cc:6:14: note:   ‘std::istream’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |         cin<<a;
      |              ^
/nix/gcc-13.2.0/include/c++/13.2.0/iomanip:180:5: note: candidate: ‘template<class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, _Setfill<_CharT>)’
  180 |     operator<<(basic_ostream<_CharT, _Traits>& __os, _Setfill<_CharT> __f)
      |     ^~~~~~~~
/nix/gcc-13.2.0/include/c++/13.2.0/iomanip:180:5: note:   template argument deduction/substitution failed:
foo.cc:6:14: note:   ‘std::istream’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |         cin<<a;
      |              ^
/nix/gcc-13.2.0/include/c++/13.2.0/iomanip:210:5: note: candidate: ‘template<class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, _Setprecision)’
  210 |     operator<<(basic_ostream<_CharT, _Traits>& __os, _Setprecision __f)
      |     ^~~~~~~~
/nix/gcc-13.2.0/include/c++/13.2.0/iomanip:210:5: note:   template argument deduction/substitution failed:
foo.cc:6:14: note:   ‘std::istream’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |         cin<<a;
      |              ^
/nix/gcc-13.2.0/include/c++/13.2.0/iomanip:240:5: note: candidate: ‘template<class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, _Setw)’
  240 |     operator<<(basic_ostream<_CharT, _Traits>& __os, _Setw __f)
      |     ^~~~~~~~
/nix/gcc-13.2.0/include/c++/13.2.0/iomanip:240:5: note:   template argument deduction/substitution failed:
foo.cc:6:14: note:   ‘std::istream’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |         cin<<a;
      |              ^
/nix/gcc-13.2.0/include/c++/13.2.0/iomanip:313:5: note: candidate: ‘template<class _CharT, class _Traits, class _MoneyT> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, _Put_money<_MoneyT>)’
  313 |     operator<<(basic_ostream<_CharT, _Traits>& __os, _Put_money<_MoneyT> __f)
      |     ^~~~~~~~
/nix/gcc-13.2.0/include/c++/13.2.0/iomanip:313:5: note:   template argument deduction/substitution failed:
foo.cc:6:14: note:   ‘std::istream’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |         cin<<a;
      |              ^
/nix/gcc-13.2.0/include/c++/13.2.0/iomanip:365:5: note: candidate: ‘template<class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, _Put_time<_CharT>)’
  365 |     operator<<(basic_ostream<_CharT, _Traits>& __os, _Put_time<_CharT> __f)
      |     ^~~~~~~~
/nix/gcc-13.2.0/include/c++/13.2.0/iomanip:365:5: note:   template argument deduction/substitution failed:
foo.cc:6:14: note:   ‘std::istream’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |         cin<<a;
      |              ^
In file included from /nix/gcc-13.2.0/include/c++/13.2.0/valarray:605,
                 from stdc++.h:166:
/nix/gcc-13.2.0/include/c++/13.2.0/bits/valarray_after.h:413:5: note: candidate: ‘template<class _Dom1, class _Dom2> std::_Expr<std::__detail::_BinClos<std::__shift_left, std::_Expr, std::_Expr, _Dom1, _Dom2>, typename std::__fun<std::__shift_left, typename _Dom1::value_type>::result_type> std::operator<<(const _Expr<_Dom1, typename _Dom1::value_type>&, const _Expr<_Dom2, typename _Dom2::value_type>&)’
  413 |     _DEFINE_EXPR_BINARY_OPERATOR(<<, struct std::__shift_left)
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/nix/gcc-13.2.0/include/c++/13.2.0/bits/valarray_after.h:413:5: note:   template argument deduction/substitution failed:
foo.cc:6:14: note:   ‘std::istream’ {aka ‘std::basic_istream<char>’} is not derived from ‘const std::_Expr<_Dom1, typename _Dom1::value_type>’
    6 |         cin<<a;
      |              ^
/nix/gcc-13.2.0/include/c++/13.2.0/bits/valarray_after.h:413:5: note: candidate: ‘template<class _Dom> std::_Expr<std::__detail::_BinClos<std::__shift_left, std::_Expr, std::_Constant, _Dom, typename _Dom::value_type>, typename std::__fun<std::__shift_left, typename _Dom1::value_type>::result_type> std::operator<<(const _Expr<_Dom1, typename _Dom1::value_type>&, const typename _Dom::value_type&)’
  413 |     _DEFINE_EXPR_BINARY_OPERATOR(<<, struct std::__shift_left)
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/nix/gcc-13.2.0/include/c++/13.2.0/bits/valarray_after.h:413:5: note:   template argument deduction/substitution failed:
foo.cc:6:14: note:   ‘std::istream’ {aka ‘std::basic_istream<char>’} is not derived from ‘const std::_Expr<_Dom1, typename _Dom1::value_type>’
    6 |         cin<<a;
      |              ^
/nix/gcc-13.2.0/include/c++/13.2.0/bits/valarray_after.h:413:5: note: candidate: ‘template<class _Dom> std::_Expr<std::__detail::_BinClos<std::__shift_left, std::_Constant, std::_Expr, typename _Dom::value_type, _Dom>, typename std::__fun<std::__shift_left, typename _Dom1::value_type>::result_type> std::operator<<(const typename _Dom::value_type&, const _Expr<_Dom1, typename _Dom1::value_type>&)’
  413 |     _DEFINE_EXPR_BINARY_OPERATOR(<<, struct std::__shift_left)
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/nix/gcc-13.2.0/include/c++/13.2.0/bits/valarray_after.h:413:5: note:   template argument deduction/substitution failed:
foo.cc:6:14: note:   mismatched types ‘const std::_Expr<_Dom1, typename _Dom1::value_type>’ and ‘int’
    6 |         cin<<a;
      |              ^
/nix/gcc-13.2.0/include/c++/13.2.0/bits/valarray_after.h:413:5: note: candidate: ‘template<class _Dom> std::_Expr<std::__detail::_BinClos<std::__shift_left, std::_Expr, std::_ValArray, _Dom, typename _Dom::value_type>, typename std::__fun<std::__shift_left, typename _Dom1::value_type>::result_type> std::operator<<(const _Expr<_Dom1, typename _Dom1::value_type>&, const valarray<typename _Dom::value_type>&)’
  413 |     _DEFINE_EXPR_BINARY_OPERATOR(<<, struct std::__shift_left)
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/nix/gcc-13.2.0/include/c++/13.2.0/bits/valarray_after.h:413:5: note:   template argument deduction/substitution failed:
foo.cc:6:14: note:   ‘std::istream’ {aka ‘std::basic_istream<char>’} is not derived from ‘const std::_Expr<_Dom1, typename _Dom1::value_type>’
    6 |         cin<<a;
      |              ^
/nix/gcc-13.2.0/include/c++/13.2.0/bits/valarray_after.h:413:5: note: candidate: ‘template<class _Dom> std::_Expr<std::__detail::_BinClos<std::__shift_left, std::_ValArray, std::_Expr, typename _Dom::value_type, _Dom>, typename std::__fun<std::__shift_left, typename _Dom1::value_type>::result_type> std::operator<<(const valarray<typename _Dom::value_type>&, const _Expr<_Dom1, typename _Dom1::value_type>&)’
  413 |     _DEFINE_EXPR_BINARY_OPERATOR(<<, struct std::__shift_left)
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~
/nix/gcc-13.2.0/include/c++/13.2.0/bits/valarray_after.h:413:5: note:   template argument deduction/substitution failed:
foo.cc:6:14: note:   mismatched types ‘const std::_Expr<_Dom1, typename _Dom1::value_type>’ and ‘int’
    6 |         cin<<a;
      |              ^
/nix/gcc-13.2.0/include/c++/13.2.0/valarray:1198:1: note: candidate: ‘template<class _Tp> std::_Expr<std::__detail::_BinClos<std::__shift_left, std::_ValArray, std::_ValArray, _Tp, _Tp>, typename std::__fun<std::__shift_left, _Tp>::result_type> std::operator<<(const valarray<_Tp>&, const valarray<_Tp>&)’
 1198 | _DEFINE_BINARY_OPERATOR(<<, __shift_left)
      | ^~~~~~~~~~~~~~~~~~~~~~~
/nix/gcc-13.2.0/include/c++/13.2.0/valarray:1198:1: note:   template argument deduction/substitution failed:
foo.cc:6:14: note:   ‘std::istream’ {aka ‘std::basic_istream<char>’} is not derived from ‘const std::valarray<_Tp>’
    6 |         cin<<a;
      |              ^
/nix/gcc-13.2.0/include/c++/13.2.0/valarray:1198:1: note: candidate: ‘template<class _Tp> std::_Expr<std::__detail::_BinClos<std::__shift_left, std::_ValArray, std::_Constant, _Tp, _Tp>, typename std::__fun<std::__shift_left, _Tp>::result_type> std::operator<<(const valarray<_Tp>&, const typename valarray<_Tp>::value_type&)’
 1198 | _DEFINE_BINARY_OPERATOR(<<, __shift_left)
      | ^~~~~~~~~~~~~~~~~~~~~~~
/nix/gcc-13.2.0/include/c++/13.2.0/valarray:1198:1: note:   template argument deduction/substitution failed:
foo.cc:6:14: note:   ‘std::istream’ {aka ‘std::basic_istream<char>’} is not derived from ‘const std::valarray<_Tp>’
    6 |         cin<<a;
      |              ^
/nix/gcc-13.2.0/include/c++/13.2.0/valarray:1198:1: note: candidate: ‘template<class _Tp> std::_Expr<std::__detail::_BinClos<std::__shift_left, std::_Constant, std::_ValArray, _Tp, _Tp>, typename std::__fun<std::__shift_left, _Tp>::result_type> std::operator<<(const typename valarray<_Tp>::value_type&, const valarray<_Tp>&)’
 1198 | _DEFINE_BINARY_OPERATOR(<<, __shift_left)
      | ^~~~~~~~~~~~~~~~~~~~~~~
/nix/gcc-13.2.0/include/c++/13.2.0/valarray:1198:1: note:   template argument deduction/substitution failed:
foo.cc:6:14: note:   mismatched types ‘const std::valarray<_Tp>’ and ‘int’
    6 |         cin<<a;
      |              ^
In file included from /nix/gcc-13.2.0/include/c++/13.2.0/random:51,
                 from stdc++.h:179:
/nix/gcc-13.2.0/include/c++/13.2.0/bits/random.h:1341:5: note: candidate: ‘template<class _RandomNumberEngine, long unsigned int __w, class _UIntType, class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, const independent_bits_engine<_RandomNumberEngine, __w, _UIntType>&)’
 1341 |     operator<<(std::basic_ostream<_CharT, _Traits>& __os,
      |     ^~~~~~~~
/nix/gcc-13.2.0/include/c++/13.2.0/bits/random.h:1341:5: note:   template argument deduction/substitution failed:
foo.cc:6:14: note:   ‘std::istream’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |         cin<<a;
      |              ^
In file included from /nix/gcc-13.2.0/include/c++/13.2.0/random:53:
/nix/gcc-13.2.0/include/c++/13.2.0/bits/random.tcc:907:5: note: candidate: ‘template<class _IntType, class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, const uniform_int_distribution<_IntType>&)’
  907 |     operator<<(std::basic_ostream<_CharT, _Traits>& __os,
      |     ^~~~~~~~
/nix/gcc-13.2.0/include/c++/13.2.0/bits/random.tcc:907:5: note:   template argument deduction/substitution failed:
foo.cc:6:14: note:   ‘std::istream’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |         cin<<a;
      |              ^
/nix/gcc-13.2.0/include/c++/13.2.0/bits/random.tcc:965:5: note: candidate: ‘template<class _RealType, class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, const uniform_real_distribution<_IntType>&)’
  965 |     operator<<(std::basic_ostream<_CharT, _Traits>& __os,
      |     ^~~~~~~~
/nix/gcc-13.2.0/include/c++/13.2.0/bits/random.tcc:965:5: note:   template argument deduction/substitution failed:
foo.cc:6:14: note:   ‘std::istream’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |         cin<<a;
      |              ^
/nix/gcc-13.2.0/include/c++/13.2.0/bits/random.tcc:2142:5: note: candidate: ‘template<class _RealType, class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, const cauchy_distribution<_RealType>&)’
 2142 |     operator<<(std::basic_ostream<_CharT, _Traits>& __os,
      |     ^~~~~~~~
/nix/gcc-13.2.0/include/c++/13.2.0/bits/random.tcc:2142:5: note:   template argument deduction/substitution failed:
foo.cc:6:14: note:   ‘std::istream’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |         cin<<a;
      |              ^
/nix/gcc-13.2.0/include/c++/13.2.0/bits/random.tcc:1026:5: note: candidate: ‘template<class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, const bernoulli_distribution&)’
 1026 |     operator<<(std::basic_ostream<_CharT, _Traits>& __os,
      |     ^~~~~~~~
/nix/gcc-13.2.0/include/c++/13.2.0/bits/random.tcc:1026:5: note:   template argument deduction/substitution failed:
foo.cc:6:14: note:   ‘std::istream’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |         cin<<a;
      |              ^
/nix/gcc-13.2.0/include/c++/13.2.0/bits/random.tcc:1107:5: note: candidate: ‘template<class _IntType, class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, const geometric_distribution<_IntType>&)’
 1107 |     operator<<(std::basic_ostream<_CharT, _Traits>& __os,
      |     ^~~~~~~~
/nix/gcc-13.2.0/include/c++/13.2.0/bits/random.tcc:1107:5: note:   template argument deduction/substitution failed:
foo.cc:6:14: note:   ‘std::istream’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |         cin<<a;
      |              ^
/nix/gcc-13.2.0/include/c++/13.2.0/bits/random.tcc:1759:5: note: candidate: ‘template<class _RealType, class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, const exponential_distribution<_RealType>&)’
 1759 |     operator<<(std::basic_ostream<_CharT, _Traits>& __os,
      |     ^~~~~~~~
/nix/gcc-13.2.0/include/c++/13.2.0/bits/random.tcc:1759:5: note:   template argument deduction/substitution failed:
foo.cc:6:14: note:   ‘std::istream’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |         cin<<a;
      |              ^
/nix/gcc-13.2.0/include/c++/13.2.0/bits/random.tcc:2536:5: note: candidate: ‘template<class _RealType, class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, const weibull_distribution<_RealType>&)’
 2536 |     operator<<(std::basic_ostream<_CharT, _Traits>& __os,
      |     ^~~~~~~~
/nix/gcc-13.2.0/include/c++/13.2.0/bits/random.tcc:2536:5: note:   template argument deduction/substitution failed:
foo.cc:6:14: note:   ‘std::istream’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |         cin<<a;
      |              ^
/nix/gcc-13.2.0/include/c++/13.2.0/bits/random.tcc:2610:5: note: candidate: ‘template<class _RealType, class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, const extreme_value_distribution<_RealType>&)’
 2610 |     operator<<(std::basic_ostream<_CharT, _Traits>& __os,
      |     ^~~~~~~~
/nix/gcc-13.2.0/include/c++/13.2.0/bits/random.tcc:2610:5: note:   template argument deduction/substitution failed:
foo.cc:6:14: note:   ‘std::istream’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |         cin<<a;
      |              ^
/nix/gcc-13.2.0/include/c++/13.2.0/bits/random.tcc:156:5: note: candidate: ‘template<class _UIntType, _UIntType __a, _UIntType __c, _UIntType __m, class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, const linear_congruential_engine<_UIntType, __a, __c, __m>&)’
  156 |     operator<<(std::basic_ostream<_CharT, _Traits>& __os,
      |     ^~~~~~~~
/nix/gcc-13.2.0/include/c++/13.2.0/bits/random.tcc:156:5: note:   template argument deduction/substitution failed:
foo.cc:6:14: note:   ‘std::istream’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |         cin<<a;
      |              ^
/nix/gcc-13.2.0/include/c++/13.2.0/bits/random.tcc:477:5: note: candidate: ‘template<class _UIntType1, long unsigned int __w1, long unsigned int __n1, long unsigned int __m1, long unsigned int __r1, _UIntType1 __a1, long unsigned int __u1, _UIntType1 __d1, long unsigned int __s1, _UIntType1 __b1, long unsigned int __t1, _UIntType1 __c1, long unsigned int __l1, _UIntType1 __f1, class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, const mersenne_twister_engine<_UIntType, __w, __n, __m, __r, __a, __u, __d, __s, __b, __t, __c, __l, __f>&)’
  477 |     operator<<(std::basic_ostream<_CharT, _Traits>& __os,
      |     ^~~~~~~~
/nix/gcc-13.2.0/include/c++/13.2.0/bits/random.tcc:477:5: note:   template argument deduction/substitution failed:
foo.cc:6:14: note:   ‘std::istream’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |         cin<<a;
      |              ^
/nix/gcc-13.2.0/include/c++/13.2.0/bits/random.tcc:632:5: note: candidate: ‘template<class _UIntType, long unsigned int __w, long unsigned int __s, long unsigned int __r, class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, const subtract_with_carry_engine<_UIntType, __w, __s, __r>&)’
  632 |     operator<<(std::basic_ostream<_CharT, _Traits>& __os,
      |     ^~~~~~~~
/nix/gcc-13.2.0/include/c++/13.2.0/bits/random.tcc:632:5: note:   template argument deduction/substitution failed:
foo.cc:6:14: note:   ‘std::istream’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |         cin<<a;
      |              ^
/nix/gcc-13.2.0/include/c++/13.2.0/bits/random.tcc:701:5: note: candidate: ‘template<class _RandomNumberEngine, long unsigned int __p, long unsigned int __r, class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, const discard_block_engine<_RandomNumberEngine, __p, __r>&)’
  701 |     operator<<(std::basic_ostream<_CharT, _Traits>& __os,
      |     ^~~~~~~~
/nix/gcc-13.2.0/include/c++/13.2.0/bits/random.tcc:701:5: note:   template argument deduction/substitution failed:
foo.cc:6:14: note:   ‘std::istream’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |         cin<<a;
      |              ^
/nix/gcc-13.2.0/include/c++/13.2.0/bits/random.tcc:863:5: note: candidate: ‘template<class _RandomNumberEngine, long unsigned int __k, class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, const shuffle_order_engine<_RandomNumberEngine, __k>&)’
  863 |     operator<<(std::basic_ostream<_CharT, _Traits>& __os,
      |     ^~~~~~~~
/nix/gcc-13.2.0/include/c++/13.2.0/bits/random.tcc:863:5: note:   template argument deduction/substitution failed:
foo.cc:6:14: note:   ‘std::istream’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |         cin<<a;
      |              ^
/nix/gcc-13.2.0/include/c++/13.2.0/bits/random.tcc:1221:5: note: candidate: ‘template<class _IntType, class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, const negative_binomial_distribution<_IntType>&)’
 1221 |     operator<<(std::basic_ostream<_CharT, _Traits>& __os,
      |     ^~~~~~~~
/nix/gcc-13.2.0/include/c++/13.2.0/bits/random.tcc:1221:5: note:   template argument deduction/substitution failed:
foo.cc:6:14: note:   ‘std::istream’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |         cin<<a;
      |              ^
/nix/gcc-13.2.0/include/c++/13.2.0/bits/random.tcc:1431:5: note: candidate: ‘template<class _IntType, class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, const poisson_distribution<_IntType>&)’
 1431 |     operator<<(std::basic_ostream<_CharT, _Traits>& __os,
      |     ^~~~~~~~
/nix/gcc-13.2.0/include/c++/13.2.0/bits/random.tcc:1431:5: note:   template argument deduction/substitution failed:
foo.cc:6:14: note:   ‘std::istream’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |         cin<<a;
      |              ^
/nix/gcc-13.2.0/include/c++/13.2.0/bits/random.tcc:1697:5: note: candidate: ‘template<class _IntType, class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, const binomial_distribution<_IntType>&)’
 1697 |     operator<<(std::basic_ostream<_CharT, _Traits>& __os,
      |     ^~~~~~~~
/nix/gcc-13.2.0/include/c++/13.2.0/bits/random.tcc:1697:5: note:   template argument deduction/substitution failed:
foo.cc:6:14: note:   ‘std::istream’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |         cin<<a;
      |              ^
/nix/gcc-13.2.0/include/c++/13.2.0/bits/random.tcc:1917:5: note: candidate: ‘template<class _RealType1, class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, const normal_distribution<_RealType>&)’
 1917 |     operator<<(std::basic_ostream<_CharT, _Traits>& __os,
      |     ^~~~~~~~
/nix/gcc-13.2.0/include/c++/13.2.0/bits/random.tcc:1917:5: note:   template argument deduction/substitution failed:
foo.cc:6:14: note:   ‘std::istream’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |         cin<<a;
      |              ^
/nix/gcc-13.2.0/include/c++/13.2.0/bits/random.tcc:1984:5: note: candidate: ‘template<class _RealType, class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, const lognormal_distribution<_RealType>&)’
 1984 |     operator<<(std::basic_ostream<_CharT, _Traits>& __os,
      |     ^~~~~~~~
/nix/gcc-13.2.0/include/c++/13.2.0/bits/random.tcc:1984:5: note:   template argument deduction/substitution failed:
foo.cc:6:14: note:   ‘std::istream’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |         cin<<a;
      |              ^
/nix/gcc-13.2.0/include/c++/13.2.0/bits/random.tcc:2056:5: note: candidate: ‘template<class _RealType, class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, const chi_squared_distribution<_RealType>&)’
 2056 |     operator<<(std::basic_ostream<_CharT, _Traits>& __os,
      |     ^~~~~~~~
/nix/gcc-13.2.0/include/c++/13.2.0/bits/random.tcc:2056:5: note:   template argument deduction/substitution failed:
foo.cc:6:14: note:   ‘std::istream’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |         cin<<a;
      |              ^
/nix/gcc-13.2.0/include/c++/13.2.0/bits/random.tcc:2217:5: note: candidate: ‘template<class _RealType, class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, const fisher_f_distribution<_RealType>&)’
 2217 |     operator<<(std::basic_ostream<_CharT, _Traits>& __os,
      |     ^~~~~~~~
/nix/gcc-13.2.0/include/c++/13.2.0/bits/random.tcc:2217:5: note:   template argument deduction/substitution failed:
foo.cc:6:14: note:   ‘std::istream’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |         cin<<a;
      |              ^
/nix/gcc-13.2.0/include/c++/13.2.0/bits/random.tcc:2291:5: note: candidate: ‘template<class _RealType, class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, const student_t_distribution<_RealType>&)’
 2291 |     operator<<(std::basic_ostream<_CharT, _Traits>& __os,
      |     ^~~~~~~~
/nix/gcc-13.2.0/include/c++/13.2.0/bits/random.tcc:2291:5: note:   template argument deduction/substitution failed:
foo.cc:6:14: note:   ‘std::istream’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |         cin<<a;
      |              ^
/nix/gcc-13.2.0/include/c++/13.2.0/bits/random.tcc:2460:5: note: candidate: ‘template<class _RealType1, class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, const gamma_distribution<_RealType>&)’
 2460 |     operator<<(std::basic_ostream<_CharT, _Traits>& __os,
      |     ^~~~~~~~
/nix/gcc-13.2.0/include/c++/13.2.0/bits/random.tcc:2460:5: note:   template argument deduction/substitution failed:
foo.cc:6:14: note:   ‘std::istream’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |         cin<<a;
      |              ^
/nix/gcc-13.2.0/include/c++/13.2.0/bits/random.tcc:2746:5: note: candidate: ‘template<class _IntType, class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, const discrete_distribution<_IntType>&)’
 2746 |     operator<<(std::basic_ostream<_CharT, _Traits>& __os,
      |     ^~~~~~~~
/nix/gcc-13.2.0/include/c++/13.2.0/bits/random.tcc:2746:5: note:   template argument deduction/substitution failed:
foo.cc:6:14: note:   ‘std::istream’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |         cin<<a;
      |              ^
/nix/gcc-13.2.0/include/c++/13.2.0/bits/random.tcc:2968:5: note: candidate: ‘template<class _RealType, class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, const piecewise_constant_distribution<_RealType>&)’
 2968 |     operator<<(std::basic_ostream<_CharT, _Traits>& __os,
      |     ^~~~~~~~
/nix/gcc-13.2.0/include/c++/13.2.0/bits/random.tcc:2968:5: note:   template argument deduction/substitution failed:
foo.cc:6:14: note:   ‘std::istream’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |         cin<<a;
      |              ^
/nix/gcc-13.2.0/include/c++/13.2.0/bits/random.tcc:3174:5: note: candidate: ‘template<class _RealType, class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, const piecewise_linear_distribution<_RealType>&)’
 3174 |     operator<<(std::basic_ostream<_CharT, _Traits>& __os,
      |     ^~~~~~~~
/nix/gcc-13.2.0/include/c++/13.2.0/bits/random.tcc:3174:5: note:   template argument deduction/substitution failed:
foo.cc:6:14: note:   ‘std::istream’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |         cin<<a;
      |              ^
In file included from stdc++.h:184:
/nix/gcc-13.2.0/include/c++/13.2.0/thread:97:5: note: candidate: ‘template<class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, thread::id)’
   97 |     operator<<(basic_ostream<_CharT, _Traits>& __out, thread::id __id)
      |     ^~~~~~~~
/nix/gcc-13.2.0/include/c++/13.2.0/thread:97:5: note:   template argument deduction/substitution failed:
foo.cc:6:14: note:   ‘std::istream’ {aka ‘std::basic_istream<char>’} is not derived from ‘std::basic_ostream<_CharT, _Traits>’
    6 |         cin<<a;
      |              ^