Language: C++

#include <bits/stdc++.h>

using namespace std;

int n;
int x[10000000000];

int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  while (cin >> n && n) {
    for (int i = 0; i < n; i++) cin > x[i];
    sort(x, x+n);
    int a, b, c, d;
    for (int i = n-1; i >= 3; i++) {
      int a = x[i], b = x[i-1], c = x[i-2], d = x[i-3];
      if (a == b && a == c && c == d) {
        cout << a*b << endl;
        break;
      }
      else if (a==b && c==d) {
        cout << a*c << endl;
        break;
      }
      if (i == 3) {
        cout << 0 << endl;
      }
    }
  }
  return 0;
}


Compiler output:
a.cc: In function 'int main()':
a.cc:12:37: error: no match for 'operator>' (operand types are 'std::istream' {aka 'std::basic_istream<char>'} and 'int')
   12 |     for (int i = 0; i < n; i++) cin > x[i];
      |                                 ~~~ ^ ~~~~
      |                                 |        |
      |                                 |        int
      |                                 std::istream {aka std::basic_istream<char>}
a.cc:12:37: note: candidate: 'operator>(int, int)' (built-in)
   12 |     for (int i = 0; i < n; i++) cin > x[i];
      |                                 ~~~~^~~~~~
a.cc:12:37: note:   no known conversion for argument 1 from 'std::istream' {aka 'std::basic_istream<char>'} to 'int'
In file included from /usr/include/c++/14/regex:68,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:181,
                 from a.cc:1:
/usr/include/c++/14/bits/regex.h:1176:5: note: candidate: 'template<class _BiIter> bool std::__cxx11::operator>(const sub_match<_BiIter>&, const sub_match<_BiIter>&)'
 1176 |     operator>(const sub_match<_BiIter>& __lhs, const sub_match<_BiIter>& __rhs)
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1176:5: note:   template argument deduction/substitution failed:
a.cc:12:42: note:   'std::istream' {aka 'std::basic_istream<char>'} is not derived from 'const std::__cxx11::sub_match<_BiIter>'
   12 |     for (int i = 0; i < n; i++) cin > x[i];
      |                                          ^
/usr/include/c++/14/bits/regex.h:1236:5: note: candidate: 'template<class _Bi_iter, class _Ch_traits, class _Ch_alloc> bool std::__cxx11::operator>(__sub_match_string<_Bi_iter, _Ch_traits, _Ch_alloc>&, const sub_match<_BiIter>&)'
 1236 |     operator>(const __sub_match_string<_Bi_iter, _Ch_traits, _Ch_alloc>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1236:5: note:   template argument deduction/substitution failed:
a.cc:12:42: note:   'std::istream' {aka 'std::basic_istream<char>'} is not derived from 'std::__cxx11::__sub_match_string<_Bi_iter, _Ch_traits, _Ch_alloc>'
   12 |     for (int i = 0; i < n; i++) cin > x[i];
      |                                          ^
/usr/include/c++/14/bits/regex.h:1329:5: note: candidate: 'template<class _Bi_iter, class _Ch_traits, class _Ch_alloc> bool std::__cxx11::operator>(const sub_match<_BiIter>&, __sub_match_string<_Bi_iter, _Ch_traits, _Ch_alloc>&)'
 1329 |     operator>(const sub_match<_Bi_iter>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1329:5: note:   template argument deduction/substitution failed:
a.cc:12:42: note:   'std::istream' {aka 'std::basic_istream<char>'} is not derived from 'const std::__cxx11::sub_match<_BiIter>'
   12 |     for (int i = 0; i < n; i++) cin > x[i];
      |                                          ^
/usr/include/c++/14/bits/regex.h:1403:5: note: candidate: 'template<class _Bi_iter> bool std::__cxx11::operator>(const typename std::iterator_traits<_Iter>::value_type*, const sub_match<_BiIter>&)'
 1403 |     operator>(typename iterator_traits<_Bi_iter>::value_type const* __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1403:5: note:   template argument deduction/substitution failed:
a.cc:12:42: note:   mismatched types 'const std::__cxx11::sub_match<_BiIter>' and 'int'
   12 |     for (int i = 0; i < n; i++) cin > x[i];
      |                                          ^
/usr/include/c++/14/bits/regex.h:1497:5: note: candidate: 'template<class _Bi_iter> bool std::__cxx11::operator>(const sub_match<_BiIter>&, const typename std::iterator_traits<_Iter>::value_type*)'
 1497 |     operator>(const sub_match<_Bi_iter>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1497:5: note:   template argument deduction/substitution failed:
a.cc:12:42: note:   'std::istream' {aka 'std::basic_istream<char>'} is not derived from 'const std::__cxx11::sub_match<_BiIter>'
   12 |     for (int i = 0; i < n; i++) cin > x[i];
      |                                          ^
/usr/include/c++/14/bits/regex.h:1573:5: note: candidate: 'template<class _Bi_iter> bool std::__cxx11::operator>(const typename std::iterator_traits<_Iter>::value_type&, const sub_match<_BiIter>&)'
 1573 |     operator>(typename iterator_traits<_Bi_iter>::value_type const& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1573:5: note:   template argument deduction/substitution failed:
a.cc:12:42: note:   mismatched types 'const std::__cxx11::sub_match<_BiIter>' and 'int'
   12 |     for (int i = 0; i < n; i++) cin > x[i];
      |                                          ^
/usr/include/c++/14/bits/regex.h:1673:5: note: candidate: 'template<class _Bi_iter> bool std::__cxx11::operator>(const sub_match<_BiIter>&, const typename std::iterator_traits<_Iter>::value_type&)'
 1673 |     operator>(const sub_match<_Bi_iter>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1673:5: note:   template argument deduction/substitution failed:
a.cc:12:42: note:   'std::istream' {aka 'std::basic_istream<char>'} is not derived from 'const std::__cxx11::sub_match<_BiIter>'
   12 |     for (int i = 0; i < n; i++) cin > x[i];
      |                                          ^
In file included from /usr/include/c++/14/bits/stl_algobase.h:64,
                 from /usr/include/c++/14/algorithm:60,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:51:
/usr/include/c++/14/bits/stl_pair.h:1058:5: note: candidate: 'template<class _T1, class _T2> constexpr bool std::operator>(const pair<_T1, _T2>&, const pair<_T1, _T2>&)'
 1058 |     operator>(const pair<_T1, _T2>& __x, const pair<_T1, _T2>& __y)
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_pair.h:1058:5: note:   template argument deduction/substitution failed:
a.cc:12:42: note:   'std::istream' {aka 'std::basic_istream<char>'} is not derived from 'const std::pair<_T1, _T2>'
   12 |     for (int i = 0; i < n; i++) cin > x[i];
      |                                          ^
In file included from /usr/include/c++/14/bits/stl_algobase.h:67:
/usr/include/c++/14/bits/stl_iterator.h:462:5: note: candidate: 'template<class _Iterator> constexpr bool std::operator>(const reverse_iterator<_Iterator>&, const reverse_iterator<_Iterator>&)'
  462 |     operator>(const reverse_iterator<_Iterator>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:462:5: note:   template argument deduction/substitution failed:
a.cc:12:42: note:   'std::istream' {aka 'std::basic_istream<char>'} is not derived from 'const std::reverse_iterator<_Iterator>'
   12 |     for (int i = 0; i < n; i++) cin > x[i];
      |                                          ^
/usr/include/c++/14/bits/stl_iterator.h:507:5: note: candidate: 'template<class _IteratorL, class _IteratorR> constexpr bool std::operator>(const reverse_iterator<_Iterator>&, const reverse_iterator<_IteratorR>&)'
  507 |     operator>(const reverse_iterator<_IteratorL>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:507:5: note:   template argument deduction/substitution failed:
a.cc:12:42: note:   'std::istream' {aka 'std::basic_istream<char>'} is not derived from 'const std::reverse_iterator<_Iterator>'
   12 |     for (int i = 0; i < n; i++) cin > x[i];
      |                                          ^
/usr/include/c++/14/bits/stl_iterator.h:1714:5: note: candidate: 'template<class _IteratorL, class _IteratorR> constexpr bool std::operator>(const move_iterator<_IteratorL>&, const move_iterator<_IteratorR>&)'
 1714 |     operator>(const move_iterator<_IteratorL>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:1714:5: note:   template argument deduction/substitution failed:
a.cc:12:42: note:   'std::istream' {aka 'std::basic_istream<char>'} is not derived from 'const std::move_iterator<_IteratorL>'
   12 |     for (int i = 0; i < n; i++) cin > x[i];
      |                                          ^
/usr/include/c++/14/bits/stl_iterator.h:1774:5: note: candidate: 'template<class _Iterator> constexpr bool std::operator>(const move_iterator<_IteratorL>&, const move_iterator<_IteratorL>&)'
 1774 |     operator>(const move_iterator<_Iterator>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:1774:5: note:   template argument deduction/substitution failed:
a.cc:12:42: note:   'std::istream' {aka 'std::basic_istream<char>'} is not derived from 'const std::move_iterator<_IteratorL>'
   12 |     for (int i = 0; i < n; i++) cin > x[i];
      |                                          ^
In file included from /usr/include/c++/14/bits/basic_string.h:47,
                 from /usr/include/c++/14/string:54,
                 from /usr/include/c++/14/bitset:52,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:52:
/usr/include/c++/14/string_view:695:5: note: candidate: 'template<class _CharT, class _Traits> constexpr bool std::operator>(basic_string_view<_CharT, _Traits>, basic_string_view<_CharT, _Traits>)'
  695 |     operator> (basic_string_view<_CharT, _Traits> __x,
      |     ^~~~~~~~
/usr/include/c++/14/string_view:695:5: note:   template argument deduction/substitution failed:
a.cc:12:42: note:   'std::basic_istream<char>' is not derived from 'std::basic_string_view<_CharT, _Traits>'
   12 |     for (int i = 0; i < n; i++) cin > x[i];
      |                                          ^
/usr/include/c++/14/string_view:702:5: note: candidate: 'template<class _CharT, class _Traits> constexpr bool std::operator>(basic_string_view<_CharT, _Traits>, __type_identity_t<basic_string_view<_CharT, _Traits> >)'
  702 |     operator> (basic_string_view<_CharT, _Traits> __x,
      |     ^~~~~~~~
/usr/include/c++/14/string_view:702:5: note:   template argument deduction/substitution failed:
a.cc:12:42: note:   'std::basic_istream<char>' is not derived from 'std::basic_string_view<_CharT, _Traits>'
   12 |     for (int i = 0; i < n; i++) cin > x[i];
      |                                          ^
/usr/include/c++/14/string_view:710:5: note: candidate: 'template<class _CharT, class _Traits> constexpr bool std::operator>(__type_identity_t<basic_string_view<_CharT, _Traits> >, basic_string_view<_CharT, _Traits>)'
  710 |     operator> (__