Language: C++

#include <bits/stdc++.h>

using namespace std;
typedef long long LL;
typedef pair<int,int> pii;

#define pb push_back
#define eb emplace_back
#define mp make_pair
#define fi first
#define se second

template<class T, class... Args>
auto create(size_t n, Args&&... args) {
	if constexpr(sizeof...(args) == 1)
		return vector<T>(n, args...);
	else
		return vector(n, create<T>(args...));
}

void __print(int x) {cerr << x;}
void __print(long x) {cerr << x;}
void __print(long long x) {cerr << x;}
void __print(unsigned x) {cerr << x;}
void __print(unsigned long x) {cerr << x;}
void __print(unsigned long long x) {cerr << x;}
void __print(float x) {cerr << x;}
void __print(double x) {cerr << x;}
void __print(long double x) {cerr << x;}
void __print(char x) {cerr << '\'' << x << '\'';}
void __print(const char *x) {cerr << '\"' << x << '\"';}
void __print(const string &x) {cerr << '\"' << x << '\"';}
void __print(bool x) {cerr << (x ? "true" : "false");}

template<typename T, typename V>
void __print(const pair<T, V> &x) {cerr << '{'; __print(x.first); cerr << ','; __print(x.second); cerr << '}';}
template<typename T>
void __print(const T &x) {int f = 0; cerr << '{'; for (auto &i: x) cerr << (f++ ? "," : ""), __print(i); cerr << "}";}
void _print() {cerr << "]\n";}
template <typename T, typename... V>
void _print(T t, V... v) {__print(t); if (sizeof...(v)) cerr << ", "; _print(v...);}

#ifdef OJ
#define debug(x...) cerr << "[" << #x << "] = ["; _print(x)
#else
#define debug(x...)
#endif
#define all(x) (x).begin(), (x).end()
#define rsort(x) sort((x).rbegin(), (x).rend())
#define sz(x) ((int)x.size())
#define fori(i, n) for (int i = 0; i < (int)(n); ++i)
#define ford(i, n, e) for (int i = (int)(n); i >= (int)(e); --i)
#define fore(i, a, b) for (int i = (int)(a); i <= (int)(b); ++i)
template<typename T> bool mmax(T &m, const T q) { if (m < q) {m = q; return true;} else return false; }
template<typename T> bool mmin(T &m, const T q) { if (m > q) {m = q; return true;} else return false; }
#define RETURN(x) do{cout << (x) << '\n'; return 0;}while(0)

const char en = '\n';
const int MOD = 0;
const int MAXN = 0;
const int INF = 1e9+1;

int solve() {
    string s;
    cin >> s;
    if(s[sz(s)-1] == 's') cout << s << "es" < en;
    else cout << s << 's' << en;
    return 0;
} 

int main(int argc, char **argv) {
#ifdef OJ
    freopen("input.txt", "rt", stdin);
    //freopen("output.txt", "wt", stdout);
#endif
    ios::sync_with_stdio(false);
    cin.tie(0);

    int ntest = 1;
    //cin >> ntest;
    fori(test, ntest) {
        //cout << "Case #" << test+1 << ": ";
        solve();
    }

    return 0;
}


Compiler output:
a.cc: In function 'int solve()':
a.cc:66:45: error: no match for 'operator<' (operand types are 'std::basic_ostream<char>' and 'const char')
   66 |     if(s[sz(s)-1] == 's') cout << s << "es" < en;
      |                           ~~~~~~~~~~~~~~~~~ ^ ~~
      |                                     |         |
      |                                     |         const char
      |                                     std::basic_ostream<char>
a.cc:66:45: note: candidate: 'operator<(int, int)' (built-in)
   66 |     if(s[sz(s)-1] == 's') cout << s << "es" < en;
      |                           ~~~~~~~~~~~~~~~~~~^~~~
a.cc:66:45: note:   no known conversion for argument 1 from 'std::basic_ostream<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:1143:5: note: candidate: 'template<class _BiIter> bool std::__cxx11::operator<(const sub_match<_BiIter>&, const sub_match<_BiIter>&)'
 1143 |     operator<(const sub_match<_BiIter>& __lhs, const sub_match<_BiIter>& __rhs)
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1143:5: note:   template argument deduction/substitution failed:
a.cc:66:47: note:   'std::basic_ostream<char>' is not derived from 'const std::__cxx11::sub_match<_BiIter>'
   66 |     if(s[sz(s)-1] == 's') cout << s << "es" < en;
      |                                               ^~
/usr/include/c++/14/bits/regex.h:1224:5: 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>&)'
 1224 |     operator<(const __sub_match_string<_Bi_iter, _Ch_traits, _Ch_alloc>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1224:5: note:   template argument deduction/substitution failed:
a.cc:66:47: note:   'std::basic_ostream<char>' is not derived from 'std::__cxx11::__sub_match_string<_Bi_iter, _Ch_traits, _Ch_alloc>'
   66 |     if(s[sz(s)-1] == 's') cout << s << "es" < en;
      |                                               ^~
/usr/include/c++/14/bits/regex.h:1317:5: 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>&)'
 1317 |     operator<(const sub_match<_Bi_iter>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1317:5: note:   template argument deduction/substitution failed:
a.cc:66:47: note:   'std::basic_ostream<char>' is not derived from 'const std::__cxx11::sub_match<_BiIter>'
   66 |     if(s[sz(s)-1] == 's') cout << s << "es" < en;
      |                                               ^~
/usr/include/c++/14/bits/regex.h:1391:5: note: candidate: 'template<class _Bi_iter> bool std::__cxx11::operator<(const typename std::iterator_traits<_Iter>::value_type*, const sub_match<_BiIter>&)'
 1391 |     operator<(typename iterator_traits<_Bi_iter>::value_type const* __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1391:5: note:   template argument deduction/substitution failed:
a.cc:66:47: note:   mismatched types 'const std::__cxx11::sub_match<_BiIter>' and 'const char'
   66 |     if(s[sz(s)-1] == 's') cout << s << "es" < en;
      |                                               ^~
/usr/include/c++/14/bits/regex.h:1485:5: note: candidate: 'template<class _Bi_iter> bool std::__cxx11::operator<(const sub_match<_BiIter>&, const typename std::iterator_traits<_Iter>::value_type*)'
 1485 |     operator<(const sub_match<_Bi_iter>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1485:5: note:   template argument deduction/substitution failed:
a.cc:66:47: note:   'std::basic_ostream<char>' is not derived from 'const std::__cxx11::sub_match<_BiIter>'
   66 |     if(s[sz(s)-1] == 's') cout << s << "es" < en;
      |                                               ^~
/usr/include/c++/14/bits/regex.h:1560:5: note: candidate: 'template<class _Bi_iter> bool std::__cxx11::operator<(const typename std::iterator_traits<_Iter>::value_type&, const sub_match<_BiIter>&)'
 1560 |     operator<(typename iterator_traits<_Bi_iter>::value_type const& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1560:5: note:   template argument deduction/substitution failed:
a.cc:66:47: note:   mismatched types 'const std::__cxx11::sub_match<_BiIter>' and 'const char'
   66 |     if(s[sz(s)-1] == 's') cout << s << "es" < en;
      |                                               ^~
/usr/include/c++/14/bits/regex.h:1660:5: note: candidate: 'template<class _Bi_iter> bool std::__cxx11::operator<(const sub_match<_BiIter>&, const typename std::iterator_traits<_Iter>::value_type&)'
 1660 |     operator<(const sub_match<_Bi_iter>& __lhs,
      |     ^~~~~~~~
/usr/include/c++/14/bits/regex.h:1660:5: note:   template argument deduction/substitution failed:
a.cc:66:47: note:   'std::basic_ostream<char>' is not derived from 'const std::__cxx11::sub_match<_BiIter>'
   66 |     if(s[sz(s)-1] == 's') cout << s << "es" < en;
      |                                               ^~
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:1045:5: note: candidate: 'template<class _T1, class _T2> constexpr bool std::operator<(const pair<_T1, _T2>&, const pair<_T1, _T2>&)'
 1045 |     operator<(const pair<_T1, _T2>& __x, const pair<_T1, _T2>& __y)
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_pair.h:1045:5: note:   template argument deduction/substitution failed:
a.cc:66:47: note:   'std::basic_ostream<char>' is not derived from 'const std::pair<_T1, _T2>'
   66 |     if(s[sz(s)-1] == 's') cout << s << "es" < en;
      |                                               ^~
In file included from /usr/include/c++/14/bits/stl_algobase.h:67:
/usr/include/c++/14/bits/stl_iterator.h:448:5: note: candidate: 'template<class _Iterator> constexpr bool std::operator<(const reverse_iterator<_Iterator>&, const reverse_iterator<_Iterator>&)'
  448 |     operator<(const reverse_iterator<_Iterator>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:448:5: note:   template argument deduction/substitution failed:
a.cc:66:47: note:   'std::basic_ostream<char>' is not derived from 'const std::reverse_iterator<_Iterator>'
   66 |     if(s[sz(s)-1] == 's') cout << s << "es" < en;
      |                                               ^~
/usr/include/c++/14/bits/stl_iterator.h:493:5: note: candidate: 'template<class _IteratorL, class _IteratorR> constexpr bool std::operator<(const reverse_iterator<_Iterator>&, const reverse_iterator<_IteratorR>&)'
  493 |     operator<(const reverse_iterator<_IteratorL>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:493:5: note:   template argument deduction/substitution failed:
a.cc:66:47: note:   'std::basic_ostream<char>' is not derived from 'const std::reverse_iterator<_Iterator>'
   66 |     if(s[sz(s)-1] == 's') cout << s << "es" < en;
      |                                               ^~
/usr/include/c++/14/bits/stl_iterator.h:1694:5: note: candidate: 'template<class _IteratorL, class _IteratorR> constexpr bool std::operator<(const move_iterator<_IteratorL>&, const move_iterator<_IteratorR>&)'
 1694 |     operator<(const move_iterator<_IteratorL>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:1694:5: note:   template argument deduction/substitution failed:
a.cc:66:47: note:   'std::basic_ostream<char>' is not derived from 'const std::move_iterator<_IteratorL>'
   66 |     if(s[sz(s)-1] == 's') cout << s << "es" < en;
      |                                               ^~
/usr/include/c++/14/bits/stl_iterator.h:1760:5: note: candidate: 'template<class _Iterator> constexpr bool std::operator<(const move_iterator<_IteratorL>&, const move_iterator<_IteratorL>&)'
 1760 |     operator<(const move_iterator<_Iterator>& __x,
      |     ^~~~~~~~
/usr/include/c++/14/bits/stl_iterator.h:1760:5: note:   template argument deduction/substitution failed:
a.cc:66:47: note:   'std::basic_ostream<char>' is not derived from 'const std::move_iterator<_IteratorL>'
   66 |     if(s[sz(s)-1] == 's') cout << s << "es" < en;
      |                                               ^~
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:673:5: note: candidate: 'template<class _CharT, class _Traits> constexpr bool std::operator<(basic_string_view<_CharT, _Traits>, basic_string_view<_CharT, _Traits>)'
  673 |     operator< (basic_string_view<_CharT, _Traits> __x,
      |     ^~~~~~~~
/usr/include/c++/14/string_view:673:5: note:   template argument deduction/substitution failed:
a.cc:66:47: note:   'std::basic_ostream<char>' is not derived from 'std::basic_string_view<_CharT, _Traits>'
   66 |     if(s[sz(s)-1] == 's') cout << s << "es" < en;
      |                                               ^~
/usr/include/c++/14/string_view:680:5: note: candidate: 'template<class _CharT, class _Traits> constexpr bool std::operator<(basic_string_view<_CharT, _Traits>, __type_identity_t<basic_string_view<_CharT, _Traits> >)'
  680 |     operator< (basic_string_view<_CharT, _Traits> __x,
      |     ^~~~~~~~
/usr/include/c++/14/string_view:680:5: note:   template argument deduction/substitution failed:
a.cc:66:47: note:   'std::basic_ostream<char>' is not derived from 'std::basic_string_view<_CharT, _Traits>'
   66 |     if(s[sz(s)-1] == 's') cout << s << "es" < en;
      |                                               ^~
/usr/include/c++/14/string_view:688:5: note: candidate: 'template<class _CharT, class _Traits> constexpr bool std::operator<(__type_identity_t<basic_string_view<_CharT, _Traits> >, basic_string_view<_CharT, _Traits>)'
  688 |     operator< (__type_identity_t<basic_string_view<_C