/in/foo.cc: In function 'int main()':
/in/foo.cc:6:17: error: no match for 'operator!=' (operand types are 'std::basic_istream<char>::__istream_type {aka std::basic_istream<char>}' and 'int')
  while(cin>>a[n]!=0) n++;
        ~~~~~~~~~^~~
/in/foo.cc:6:17: note: candidate: operator!=(int, int) <built-in>
/in/foo.cc:6:17: note:   no known conversion for argument 1 from 'std::basic_istream<char>::__istream_type {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:951:5: 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:951:5: note:   template argument deduction/substitution failed:
/in/foo.cc:6:19: note:   'std::basic_istream<char>::__istream_type {aka std::basic_istream<char>}' is not derived from 'const std::__cxx11::sub_match<_BiIter>'
  while(cin>>a[n]!=0) n++;
                   ^
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:1029:5: 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:1029:5: note:   template argument deduction/substitution failed:
/in/foo.cc:6:19: note:   'std::basic_istream<char>::__istream_type {aka std::basic_istream<char>}' is not derived from 'std::__cxx11::__sub_match_string<_Bi_iter, _Ch_traits, _Ch_alloc>'
  while(cin>>a[n]!=0) n++;
                   ^
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:1109:5: 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:1109:5: note:   template argument deduction/substitution failed:
/in/foo.cc:6:19: note:   'std::basic_istream<char>::__istream_type {aka std::basic_istream<char>}' is not derived from 'const std::__cxx11::sub_match<_BiIter>'
  while(cin>>a[n]!=0) n++;
                   ^
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:1186:5: 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:1186:5: note:   template argument deduction/substitution failed:
/in/foo.cc:6:19: note:   mismatched types 'const std::__cxx11::sub_match<_BiIter>' and 'int'
  while(cin>>a[n]!=0) n++;
                   ^
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:1260:5: 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:1260:5: note:   template argument deduction/substitution failed:
/in/foo.cc:6:19: note:   'std::basic_istream<char>::__istream_type {aka std::basic_istream<char>}' is not derived from 'const std::__cxx11::sub_match<_BiIter>'
  while(cin>>a[n]!=0) n++;
                   ^
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:1337:5: 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:1337:5: note:   template argument deduction/substitution failed:
/in/foo.cc:6:19: note:   mismatched types 'const std::__cxx11::sub_match<_BiIter>' and 'int'
  while(cin>>a[n]!=0) n++;
                   ^
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:1417:5: 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:1417:5: note:   template argument deduction/substitution failed:
/in/foo.cc:6:19: note:   'std::basic_istream<char>::__istream_type {aka std::basic_istream<char>}' is not derived from 'const std::__cxx11::sub_match<_BiIter>'
  while(cin>>a[n]!=0) n++;
                   ^
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:1944:5: note: candidate: template<class _Bi_iter, class _Alloc> bool std::__cxx11::operator!=(const std::__cxx11::match_results<_BiIter, _Alloc>&, const std::__cxx11::match_results<_BiIter, _Alloc>&)
     operator!=(const match_results<_Bi_iter, _Alloc>& __m1,
     ^~~~~~~~
/usr/include/c++/6/bits/regex.h:1944:5: note:   template argument deduction/substitution failed:
/in/foo.cc:6:19: note:   'std::basic_istream<char>::__istream_type {aka std::basic_istream<char>}' is not derived from 'const std::__cxx11::match_results<_BiIter, _Alloc>'
  while(cin>>a[n]!=0) n++;
                   ^
In file included from /usr/include/c++/6/unordered_set:48:0,
                 from /usr/include/x86_64-linux-gnu/c++/6/bits/stdc++.h:118,
                 from /in/foo.cc:1:
/usr/include/c++/6/bits/unordered_set.h:1429:5: note: candidate: template<class _Value, class _Hash, class _Pred, class _Alloc> bool std::operator!=(const std::unordered_multiset<_Value, _Hash, _Pred, _Alloc>&, const std::unordered_multiset<_Value, _Hash, _Pred, _Alloc>&)
     operator!=(const unordered_multiset<_Value, _Hash, _Pred, _Alloc>& __x,
     ^~~~~~~~
/usr/include/c++/6/bits/unordered_set.h:1429:5: note:   template argument deduction/substitution failed:
/in/foo.cc:6:19: note:   'std::basic_istream<char>::__istream_type {aka std::basic_istream<char>}' is not derived from 'const std::unordered_multiset<_Value, _Hash, _Pred, _Alloc>'
  while(cin>>a[n]!=0) n++;
                   ^
In file included from /usr/include/c++/6/unordered_set:48:0,
                 from /usr/include/x86_64-linux-gnu/c++/6/bits/stdc++.h:118,
                 from /in/foo.cc:1:
/usr/include/c++/6/bits/unordered_set.h:1417:5: note: candidate: template<class _Value, class _Hash, class _Pred, class _Alloc> bool std::operator!=(const std::unordered_set<_Value, _Hash, _Pred, _Alloc>&, const std::unordered_set<_Value, _Hash, _Pred, _Alloc>&)
     operator!=(const unordered_set<_Value, _Hash, _Pred, _Alloc>& __x,
     ^~~~~~~~
/usr/include/c++/6/bits/unordered_set.h:1417:5: note:   template argument deduction/substitution failed:
/in/foo.cc:6:19: note:   'std::basic_istream<char>::__istream_type {aka std::basic_istream<char>}' is not derived from 'const std::unordere