/in/foo.cc: In function 'int main()':
/in/foo.cc:8:13: error: no match for 'operator<<' (operand types are 'std::istream' {aka 'std::basic_istream<char>'} and 'int')
    8 |         cin << a << b << c;
      |         ~~~ ^~ ~
      |         |      |
      |         |      int
      |         std::istream {aka std::basic_istream<char>}
/in/foo.cc:8:13: note: candidate: 'operator<<(int, int)' (built-in)
    8 |         cin << a << b << c;
      |         ~~~~^~~~
/in/foo.cc:8:13: note:   no known conversion for argument 1 from 'std::istream' {aka 'std::basic_istream<char>'} to 'int'
In file included from /usr/include/c++/12/string:53,
                 from /usr/include/c++/12/bits/locale_classes.h:40,
                 from /usr/include/c++/12/bits/ios_base.h:41,
                 from /usr/include/c++/12/ios:42,
                 from /usr/include/c++/12/ostream:38,
                 from /usr/include/c++/12/iostream:39,
                 from /in/foo.cc:1:
/usr/include/c++/12/bits/basic_string.h:3883:5: 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>&)'
 3883 |     operator<<(basic_ostream<_CharT, _Traits>& __os,
      |     ^~~~~~~~
/usr/include/c++/12/bits/basic_string.h:3883:5: note:   template argument deduction/substitution failed:
/in/foo.cc:8:16: note:   'std::istream' {aka 'std::basic_istream<char>'} is not derived from 'std::basic_ostream<_CharT, _Traits>'
    8 |         cin << a << b << c;
      |                ^
In file included from /usr/include/c++/12/bits/ios_base.h:46:
/usr/include/c++/12/system_error:279:5: note: candidate: 'template<class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, const error_code&)'
  279 |     operator<<(basic_ostream<_CharT, _Traits>& __os, const error_code& __e)
      |     ^~~~~~~~
/usr/include/c++/12/system_error:279:5: note:   template argument deduction/substitution failed:
/in/foo.cc:8:16: note:   'std::istream' {aka 'std::basic_istream<char>'} is not derived from 'std::basic_ostream<_CharT, _Traits>'
    8 |         cin << a << b << c;
      |                ^
/usr/include/c++/12/ostream:507:5: note: candidate: 'template<class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, _CharT)'
  507 |     operator<<(basic_ostream<_CharT, _Traits>& __out, _CharT __c)
      |     ^~~~~~~~
/usr/include/c++/12/ostream:507:5: note:   template argument deduction/substitution failed:
/in/foo.cc:8:16: note:   'std::istream' {aka 'std::basic_istream<char>'} is not derived from 'std::basic_ostream<_CharT, _Traits>'
    8 |         cin << a << b << c;
      |                ^
/usr/include/c++/12/ostream:517:5: note: candidate: 'template<class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, char)'
  517 |     operator<<(basic_ostream<_CharT, _Traits>& __out, char __c)
      |     ^~~~~~~~
/usr/include/c++/12/ostream:517:5: note:   template argument deduction/substitution failed:
/in/foo.cc:8:16: note:   'std::istream' {aka 'std::basic_istream<char>'} is not derived from 'std::basic_ostream<_CharT, _Traits>'
    8 |         cin << a << b << c;
      |                ^
/usr/include/c++/12/ostream:523:5: note: candidate: 'template<class _Traits> std::basic_ostream<char, _Traits>& std::operator<<(basic_ostream<char, _Traits>&, char)'
  523 |     operator<<(basic_ostream<char, _Traits>& __out, char __c)
      |     ^~~~~~~~
/usr/include/c++/12/ostream:523:5: note:   template argument deduction/substitution failed:
/in/foo.cc:8:16: note:   'std::istream' {aka 'std::basic_istream<char>'} is not derived from 'std::basic_ostream<char, _Traits>'
    8 |         cin << a << b << c;
      |                ^
/usr/include/c++/12/ostream:534:5: note: candidate: 'template<class _Traits> std::basic_ostream<char, _Traits>& std::operator<<(basic_ostream<char, _Traits>&, signed char)'
  534 |     operator<<(basic_ostream<char, _Traits>& __out, signed char __c)
      |     ^~~~~~~~
/usr/include/c++/12/ostream:534:5: note:   template argument deduction/substitution failed:
/in/foo.cc:8:16: note:   'std::istream' {aka 'std::basic_istream<char>'} is not derived from 'std::basic_ostream<char, _Traits>'
    8 |         cin << a << b << c;
      |                ^
/usr/include/c++/12/ostream:539:5: note: candidate: 'template<class _Traits> std::basic_ostream<char, _Traits>& std::operator<<(basic_ostream<char, _Traits>&, unsigned char)'
  539 |     operator<<(basic_ostream<char, _Traits>& __out, unsigned char __c)
      |     ^~~~~~~~
/usr/include/c++/12/ostream:539:5: note:   template argument deduction/substitution failed:
/in/foo.cc:8:16: note:   'std::istream' {aka 'std::basic_istream<char>'} is not derived from 'std::basic_ostream<char, _Traits>'
    8 |         cin << a << b << c;
      |                ^
/usr/include/c++/12/ostream:598:5: note: candidate: 'template<class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, const _CharT*)'
  598 |     operator<<(basic_ostream<_CharT, _Traits>& __out, const _CharT* __s)
      |     ^~~~~~~~
/usr/include/c++/12/ostream:598:5: note:   template argument deduction/substitution failed:
/in/foo.cc:8:16: note:   'std::istream' {aka 'std::basic_istream<char>'} is not derived from 'std::basic_ostream<_CharT, _Traits>'
    8 |         cin << a << b << c;
      |                ^
In file included from /usr/include/c++/12/ostream:833:
/usr/include/c++/12/bits/ostream.tcc:302:5: note: candidate: 'template<class _CharT, class _Traits> std::basic_ostream<_CharT, _Traits>& std::operator<<(basic_ostream<_CharT, _Traits>&, const char*)'
  302 |     operator<<(basic_ostream<_CharT, _Traits>& __out, const char* __s)
      |     ^~~~~~~~
/usr/include/c++/12/bits/ostream.tcc:302:5: note:   template argument deduction/substitution failed:
/in/foo.cc:8:16: note:   'std::istream' {aka 'std::basic_istream<char>'} is not derived from 'std::basic_ostream<_CharT, _Traits>'
    8 |         cin << a << b << c;
      |                ^
/usr/include/c++/12/ostream:615:5: note: candidate: 'template<class _Traits> std::basic_ostream<char, _Traits>& std::operator<<(basic_ostream<char, _Traits>&, const char*)'
  615 |     operator<<(basic_ostream<char, _Traits>& __out, const char* __s)
      |     ^~~~~~~~
/usr/include/c++/12/ostream:615:5: note:   template argument deduction/substitution failed:
/in/foo.cc:8:16: note:   'std::istream' {aka 'std::basic_istream<char>'} is not derived from 'std::basic_ostream<char, _Traits>'
    8 |         cin << a << b << c;
      |                ^
/usr/include/c++/12/ostream:628:5: note: candidate: 'template<class _Traits> std::basic_ostream<char, _Traits>& std::operator<<(basic_ostream<char, _Traits>&, const signed char*)'
  628 |     operator<<(basic_ostream<char, _Traits>& __out, const signed char* __s)
      |     ^~~~~~~~
/usr/include/c++/12/ostream:628:5: note:   template argument deduction/substitution failed:
/in/foo.cc:8:16: note:   'std::istream' {aka 'std::basic_istream<char>'} is not derived from 'std::basic_ostream<char, _Traits>'
    8 |         cin << a << b << c;
      |                ^
/usr/include/c++/12/ostream:633:5: note: candidate: 'template<class _Traits> std::basic_ostream<char, _Traits>& std::operator<<(basic_ostream<char, _Traits>&, const unsigned char*)'
  633 |     operator<<(basic_ostream<char, _Traits>& __out, const unsigned char* __s)
      |     ^~~~~~~~
/usr/include/c++/12/ostream:633:5: note:   template argument deduction/substitution failed:
/in/foo.cc:8:16: note:   'std::istream' {aka 'std::basic_istream<char>'} is not derived from 'std::basic_ostream<char, _Traits>'
    8 |         cin << a << b << c;
      |                ^
/usr/include/c++/12/ostream:754:5: note: candidate: 'template<class _Ostream, class _Tp> _Ostream&& std::operator<<(_Ostream&&, const _Tp&)'
  754 |     operator<<(_Ostream&& __os, const _Tp& __x)
      |     ^~~~~~~~
/usr/include/c++