Language: C++

#include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for(int i=0;i<(int)(n);i++)
#define rrep(i, n) for(int i=((int)(n));i>0;i--)
#define FOR(i, m, n) for(int i = m; i < n; i++)	
#define SORT(c) sort((c).begin(),(c).end())
#define REVERSE(c) reverse((c).begin(),(c).end())
#define REVSORT(c) SORT(c);REVERSE(c)
#define ALL(x) (x).begin(),(x).end()
#define LOOP while(true)
#define INF 1e9
const long long MOD = 1000000007;
typedef long long ll;

int main(){
	int N;
	set<char> H;
	rep(i, N){
		char S;
		cin >> S;
		H.insert(H);
	}
	cout << ((H.size() == 3) ? "Three" : "Four") << endl;
}

Compiler output:
a.cc: In function 'int main()':
a.cc:21:25: error: no matching function for call to 'std::set<char>::insert(std::set<char>&)'
   21 |                 H.insert(H);
      |                 ~~~~~~~~^~~
In file included from /usr/include/c++/14/set:63,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:158,
                 from a.cc:1:
/usr/include/c++/14/bits/stl_set.h:568:9: note: candidate: 'template<class _InputIterator> void std::set<_Key, _Compare, _Alloc>::insert(_InputIterator, _InputIterator) [with _Key = char; _Compare = std::less<char>; _Alloc = std::allocator<char>]'
  568 |         insert(_InputIterator __first, _InputIterator __last)
      |         ^~~~~~
/usr/include/c++/14/bits/stl_set.h:568:9: note:   candidate expects 2 arguments, 1 provided
/usr/include/c++/14/bits/stl_set.h:511:7: note: candidate: 'std::pair<typename std::_Rb_tree<_Key, _Key, std::_Identity<_Tp>, _Compare, typename __gnu_cxx::__alloc_traits<_Alloc>::rebind<_Key>::other>::const_iterator, bool> std::set<_Key, _Compare, _Alloc>::insert(const value_type&) [with _Key = char; _Compare = std::less<char>; _Alloc = std::allocator<char>; typename std::_Rb_tree<_Key, _Key, std::_Identity<_Tp>, _Compare, typename __gnu_cxx::__alloc_traits<_Alloc>::rebind<_Key>::other>::const_iterator = std::_Rb_tree<char, char, std::_Identity<char>, std::less<char>, std::allocator<char> >::const_iterator; typename __gnu_cxx::__alloc_traits<_Alloc>::rebind<_Key>::other = std::allocator<char>; typename __gnu_cxx::__alloc_traits<_Alloc>::rebind<_Key> = __gnu_cxx::__alloc_traits<std::allocator<char>, char>::rebind<char>; typename _Alloc::value_type = char; value_type = char]'
  511 |       insert(const value_type& __x)
      |       ^~~~~~
/usr/include/c++/14/bits/stl_set.h:511:32: note:   no known conversion for argument 1 from 'std::set<char>' to 'const std::set<char>::value_type&' {aka 'const char&'}
  511 |       insert(const value_type& __x)
      |              ~~~~~~~~~~~~~~~~~~^~~
/usr/include/c++/14/bits/stl_set.h:520:7: note: candidate: 'std::pair<typename std::_Rb_tree<_Key, _Key, std::_Identity<_Tp>, _Compare, typename __gnu_cxx::__alloc_traits<_Alloc>::rebind<_Key>::other>::const_iterator, bool> std::set<_Key, _Compare, _Alloc>::insert(value_type&&) [with _Key = char; _Compare = std::less<char>; _Alloc = std::allocator<char>; typename std::_Rb_tree<_Key, _Key, std::_Identity<_Tp>, _Compare, typename __gnu_cxx::__alloc_traits<_Alloc>::rebind<_Key>::other>::const_iterator = std::_Rb_tree<char, char, std::_Identity<char>, std::less<char>, std::allocator<char> >::const_iterator; typename __gnu_cxx::__alloc_traits<_Alloc>::rebind<_Key>::other = std::allocator<char>; typename __gnu_cxx::__alloc_traits<_Alloc>::rebind<_Key> = __gnu_cxx::__alloc_traits<std::allocator<char>, char>::rebind<char>; typename _Alloc::value_type = char; value_type = char]'
  520 |       insert(value_type&& __x)
      |       ^~~~~~
/usr/include/c++/14/bits/stl_set.h:520:27: note:   no known conversion for argument 1 from 'std::set<char>' to 'std::set<char>::value_type&&' {aka 'char&&'}
  520 |       insert(value_type&& __x)
      |              ~~~~~~~~~~~~~^~~
/usr/include/c++/14/bits/stl_set.h:548:7: note: candidate: 'std::set<_Key, _Compare, _Alloc>::iterator std::set<_Key, _Compare, _Alloc>::insert(const_iterator, const value_type&) [with _Key = char; _Compare = std::less<char>; _Alloc = std::allocator<char>; iterator = std::_Rb_tree<char, char, std::_Identity<char>, std::less<char>, std::allocator<char> >::const_iterator; const_iterator = std::_Rb_tree<char, char, std::_Identity<char>, std::less<char>, std::allocator<char> >::const_iterator; value_type = char]'
  548 |       insert(const_iterator __position, const value_type& __x)
      |       ^~~~~~
/usr/include/c++/14/bits/stl_set.h:548:7: note:   candidate expects 2 arguments, 1 provided
/usr/include/c++/14/bits/stl_set.h:553:7: note: candidate: 'std::set<_Key, _Compare, _Alloc>::iterator std::set<_Key, _Compare, _Alloc>::insert(const_iterator, value_type&&) [with _Key = char; _Compare = std::less<char>; _Alloc = std::allocator<char>; iterator = std::_Rb_tree<char, char, std::_Identity<char>, std::less<char>, std::allocator<char> >::const_iterator; const_iterator = std::_Rb_tree<char, char, std::_Identity<char>, std::less<char>, std::allocator<char> >::const_iterator; value_type = char]'
  553 |       insert(const_iterator __position, value_type&& __x)
      |       ^~~~~~
/usr/include/c++/14/bits/stl_set.h:553:7: note:   candidate expects 2 arguments, 1 provided
/usr/include/c++/14/bits/stl_set.h:580:7: note: candidate: 'void std::set<_Key, _Compare, _Alloc>::insert(std::initializer_list<_Tp>) [with _Key = char; _Compare = std::less<char>; _Alloc = std::allocator<char>]'
  580 |       insert(initializer_list<value_type> __l)
      |       ^~~~~~
/usr/include/c++/14/bits/stl_set.h:580:43: note:   no known conversion for argument 1 from 'std::set<char>' to 'std::initializer_list<char>'
  580 |       insert(initializer_list<value_type> __l)
      |              ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~
/usr/include/c++/14/bits/stl_set.h:600:7: note: candidate: 'std::set<_Key, _Compare, _Alloc>::insert_return_type std::set<_Key, _Compare, _Alloc>::insert(node_type&&) [with _Key = char; _Compare = std::less<char>; _Alloc = std::allocator<char>; insert_return_type = std::_Rb_tree<char, char, std::_Identity<char>, std::less<char>, std::allocator<char> >::insert_return_type; node_type = std::_Rb_tree<char, char, std::_Identity<char>, std::less<char>, std::allocator<char> >::node_type]'
  600 |       insert(node_type&& __nh)
      |       ^~~~~~
/usr/include/c++/14/bits/stl_set.h:600:26: note:   no known conversion for argument 1 from 'std::set<char>' to 'std::set<char>::node_type&&' {aka 'std::_Rb_tree<char, char, std::_Identity<char>, std::less<char>, std::allocator<char> >::node_type&&'}
  600 |       insert(node_type&& __nh)
      |              ~~~~~~~~~~~~^~~~
/usr/include/c++/14/bits/stl_set.h:605:7: note: candidate: 'std::set<_Key, _Compare, _Alloc>::iterator std::set<_Key, _Compare, _Alloc>::insert(const_iterator, node_type&&) [with _Key = char; _Compare = std::less<char>; _Alloc = std::allocator<char>; iterator = std::_Rb_tree<char, char, std::_Identity<char>, std::less<char>, std::allocator<char> >::const_iterator; const_iterator = std::_Rb_tree<char, char, std::_Identity<char>, std::less<char>, std::allocator<char> >::const_iterator; node_type = std::_Rb_tree<char, char, std::_Identity<char>, std::less<char>, std::allocator<char> >::node_type]'
  605 |       insert(const_iterator __hint, node_type&& __nh)
      |       ^~~~~~
/usr/include/c++/14/bits/stl_set.h:605:7: note:   candidate expects 2 arguments, 1 provided