/in/foo.cc: In function 'int main()':
/in/foo.cc:6:27: error: no match for 'operator>' (operand types are 'std::istream {aka std::basic_istream<char>}' and 'int')
  for(int i=1;i<=n;i++) cin>a[i];
                        ~~~^~~~~
/in/foo.cc:6:27: note: candidate: operator>(int, int) <built-in>
/in/foo.cc:6:27: note:   no known conversion for argument 1 from 'std::istream {aka std::basic_istream<char>}' to 'int'
In file included from /usr/include/c++/6/regex:62:0,
                 from /usr/include/x86_64-linux-gnu/c++/6/bits/stdc++.h:110,
                 from /in/foo.cc:1:
/usr/include/c++/6/bits/regex.h:995:5: note: candidate: template<class _BiIter> bool std::__cxx11::operator>(const std::__cxx11::sub_match<_BiIter>&, const std::__cxx11::sub_match<_BiIter>&)
     operator>(const sub_match<_BiIter>& __lhs, const sub_match<_BiIter>& __rhs)
     ^~~~~~~~
/usr/include/c++/6/bits/regex.h:995:5: note:   template argument deduction/substitution failed:
/in/foo.cc:6:31: note:   'std::istream {aka std::basic_istream<char>}' is not derived from 'const std::__cxx11::sub_match<_BiIter>'
  for(int i=1;i<=n;i++) cin>a[i];
                               ^
In file included from /usr/include/c++/6/regex:62:0,
                 from /usr/include/x86_64-linux-gnu/c++/6/bits/stdc++.h:110,
                 from /in/foo.cc:1:
/usr/include/c++/6/bits/regex.h:1056:5: note: candidate: template<class _Bi_iter, class _Ch_traits, class _Ch_alloc> bool std::__cxx11::operator>(std::__cxx11::__sub_match_string<_Bi_iter, _Ch_traits, _Ch_alloc>&, const std::__cxx11::sub_match<_BiIter>&)
     operator>(const __sub_match_string<_Bi_iter, _Ch_traits, _Ch_alloc>& __lhs,
     ^~~~~~~~
/usr/include/c++/6/bits/regex.h:1056:5: note:   template argument deduction/substitution failed:
/in/foo.cc:6:31: note:   'std::istream {aka std::basic_istream<char>}' is not derived from 'std::__cxx11::__sub_match_string<_Bi_iter, _Ch_traits, _Ch_alloc>'
  for(int i=1;i<=n;i++) cin>a[i];
                               ^
In file included from /usr/include/c++/6/regex:62:0,
                 from /usr/include/x86_64-linux-gnu/c++/6/bits/stdc++.h:110,
                 from /in/foo.cc:1:
/usr/include/c++/6/bits/regex.h:1136:5: note: candidate: template<class _Bi_iter, class _Ch_traits, class _Ch_alloc> bool std::__cxx11::operator>(const std::__cxx11::sub_match<_BiIter>&, std::__cxx11::__sub_match_string<_Bi_iter, _Ch_traits, _Ch_alloc>&)
     operator>(const sub_match<_Bi_iter>& __lhs,
     ^~~~~~~~
/usr/include/c++/6/bits/regex.h:1136:5: note:   template argument deduction/substitution failed:
/in/foo.cc:6:31: note:   'std::istream {aka std::basic_istream<char>}' is not derived from 'const std::__cxx11::sub_match<_BiIter>'
  for(int i=1;i<=n;i++) cin>a[i];
                               ^
In file included from /usr/include/c++/6/regex:62:0,
                 from /usr/include/x86_64-linux-gnu/c++/6/bits/stdc++.h:110,
                 from /in/foo.cc:1:
/usr/include/c++/6/bits/regex.h:1210:5: note: candidate: template<class _Bi_iter> bool std::__cxx11::operator>(const typename std::iterator_traits<_Iter>::value_type*, const std::__cxx11::sub_match<_BiIter>&)
     operator>(typename iterator_traits<_Bi_iter>::value_type const* __lhs,
     ^~~~~~~~
/usr/include/c++/6/bits/regex.h:1210:5: note:   template argument deduction/substitution failed:
/in/foo.cc:6:31: note:   mismatched types 'const std::__cxx11::sub_match<_BiIter>' and 'int'
  for(int i=1;i<=n;i++) cin>a[i];
                               ^
In file included from /usr/include/c++/6/regex:62:0,
                 from /usr/include/x86_64-linux-gnu/c++/6/bits/stdc++.h:110,
                 from /in/foo.cc:1:
/usr/include/c++/6/bits/regex.h:1284:5: note: candidate: template<class _Bi_iter> bool std::__cxx11::operator>(const std::__cxx11::sub_match<_BiIter>&, const typename std::iterator_traits<_Iter>::value_type*)
     operator>(const sub_match<_Bi_iter>& __lhs,
     ^~~~~~~~
/usr/include/c++/6/bits/regex.h:1284:5: note:   template argument deduction/substitution failed:
/in/foo.cc:6:31: note:   'std::istream {aka std::basic_istream<char>}' is not derived from 'const std::__cxx11::sub_match<_BiIter>'
  for(int i=1;i<=n;i++) cin>a[i];
                               ^
In file included from /usr/include/c++/6/regex:62:0,
                 from /usr/include/x86_64-linux-gnu/c++/6/bits/stdc++.h:110,
                 from /in/foo.cc:1:
/usr/include/c++/6/bits/regex.h:1364:5: note: candidate: template<class _Bi_iter> bool std::__cxx11::operator>(const typename std::iterator_traits<_Iter>::value_type&, const std::__cxx11::sub_match<_BiIter>&)
     operator>(typename iterator_traits<_Bi_iter>::value_type const& __lhs,
     ^~~~~~~~
/usr/include/c++/6/bits/regex.h:1364:5: note:   template argument deduction/substitution failed:
/in/foo.cc:6:31: note:   mismatched types 'const std::__cxx11::sub_match<_BiIter>' and 'int'
  for(int i=1;i<=n;i++) cin>a[i];
                               ^
In file included from /usr/include/c++/6/regex:62:0,
                 from /usr/include/x86_64-linux-gnu/c++/6/bits/stdc++.h:110,
                 from /in/foo.cc:1:
/usr/include/c++/6/bits/regex.h:1444:5: note: candidate: template<class _Bi_iter> bool std::__cxx11::operator>(const std::__cxx11::sub_match<_BiIter>&, const typename std::iterator_traits<_Iter>::value_type&)
     operator>(const sub_match<_Bi_iter>& __lhs,
     ^~~~~~~~
/usr/include/c++/6/bits/regex.h:1444:5: note:   template argument deduction/substitution failed:
/in/foo.cc:6:31: note:   'std::istream {aka std::basic_istream<char>}' is not derived from 'const std::__cxx11::sub_match<_BiIter>'
  for(int i=1;i<=n;i++) cin>a[i];
                               ^
In file included from /usr/include/c++/6/future:40:0,
                 from /usr/include/x86_64-linux-gnu/c++/6/bits/stdc++.h:105,
                 from /in/foo.cc:1:
/usr/include/c++/6/thread:243:3: note: candidate: bool std::operator>(std::thread::id, std::thread::id)
   operator>(thread::id __x, thread::id __y) noexcept
   ^~~~~~~~
/usr/include/c++/6/thread:243:3: note:   no known conversion for argument 1 from 'std::istream {aka std::basic_istream<char>}' to 'std::thread::id'
In file included from /usr/include/c++/6/forward_list:38:0,
                 from /usr/include/x86_64-linux-gnu/c++/6/bits/stdc++.h:104,
                 from /in/foo.cc:1:
/usr/include/c++/6/bits/forward_list.h:1391:5: note: candidate: template<class _Tp, class _Alloc> bool std::operator>(const std::forward_list<_Tp, _Alloc>&, const std::forward_list<_Tp, _Alloc>&)
     operator>(const forward_list<_Tp, _Alloc>& __lx,
     ^~~~~~~~
/usr/include/c++/6/bits/forward_list.h:1391:5: note:   template argument deduction/substitution failed:
/in/foo.cc:6:31: note:   'std::istream {aka std::basic_istream<char>}' is not derived from 'const std::forward_list<_Tp, _Alloc>'
  for(int i=1;i<=n;i++) cin>a[i];
                               ^
In file included from /usr/include/x86_64-linux-gnu/c++/6/bits/stdc++.h:95:0,
                 from /in/foo.cc:1:
/usr/include/c++/6/valarray:1182:1: note: candidate: template<class _Tp> std::_Expr<std::_BinClos<std::__greater, std::_Constant, std::_ValArray, _Tp, _Tp>, typename std::__fun<std::__greater, _Tp>::result_type> std::operator>(const _Tp&, const std::valarray<_Tp>&)
 _DEFINE_BINARY_OPERATOR(>, __greater)
 ^
/usr/include/c++/6/valarray:1182:1: note:   template argument deduction/substitution failed:
/in/foo.cc:6:31: note:   mismatched types 'const std::valarray<_Tp>' and 'int'
  for(int i=1;i<=n;i++) cin>a[i];
                               ^
In file included from /usr/include/x86_64-linux-gnu/c++/6/bits/stdc++.h:95:0,
                 from /in/foo.cc:1:
/usr/include/c++/6/valarray:1182:1: note: candidate: template<class _Tp> std::_Expr<std::_BinClos<std::__greater, std::_ValArray, std::_Constant, _Tp, _Tp>, typename std::__fun<std::__greater, _Tp>::result_type> std::operator>(const std::valarray<_Tp>&, const _Tp&)
 _DEFINE_BINARY_OPERATOR(>, __greater)
 ^
/usr/include/c++/6/valarray:1182:1: note:   template argument deduction/substitution failed:
/in/foo.cc:6:31: note:   'std::istream {aka std::basic_istream<char>}' is not derived from