Language: C++

//#define _GLIBCXX_DEBUG
#include<bits/stdc++.h>
#define PI 3.14159265359
using namespace std;
#define rep(i, n) for (ll i = 0; i < (ll)(n); i++)
const long long INF= 1e+18+1;
typedef long long ll;
typedef vector<ll> vl;
typedef vector<vector<ll> >vvl;
typedef pair<ll,ll> P;
typedef tuple<ll,ll,ll> T;
const ll MOD=1000000007LL;
string abc="abcdefghijklmnopqrstuvwxyz";
string ABC="ABCDEFGHIJKLMNOPQRSTUVWXYZ";
int main(){
  ll n;cin>>n;string s;cin>>s;
  set<char,ll>S;
  rep(i,n)S.insert(s[i]);
  if(S.size()==3)cout<<"Three"<<endl;
  else cout<<"Four"<<endl;
}

Compiler output:
In file included from /usr/include/c++/14/map:62,
                 from /usr/include/x86_64-linux-gnu/c++/14/bits/stdc++.h:152,
                 from a.cc:2:
/usr/include/c++/14/bits/stl_tree.h: In instantiation of 'std::pair<std::_Rb_tree_node_base*, std::_Rb_tree_node_base*> std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::_M_get_insert_unique_pos(const key_type&) [with _Key = char; _Val = char; _KeyOfValue = std::_Identity<char>; _Compare = long long int; _Alloc = std::allocator<char>; key_type = char]':
/usr/include/c++/14/bits/stl_tree.h:2169:4:   required from 'std::pair<std::_Rb_tree_iterator<_Val>, bool> std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::_M_insert_unique(_Arg&&) [with _Arg = const char&; _Key = char; _Val = char; _KeyOfValue = std::_Identity<char>; _Compare = long long int; _Alloc = std::allocator<char>]'
 2169 |         = _M_get_insert_unique_pos(_KeyOfValue()(__v));
      |           ^~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/stl_set.h:514:25:   required from '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 = long long int; _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>, long long int, 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]'
  514 |           _M_t._M_insert_unique(__x);
      |           ~~~~~~~~~~~~~~~~~~~~~^~~~~
a.cc:18:19:   required from here
   18 |   rep(i,n)S.insert(s[i]);
      |           ~~~~~~~~^~~~~~
/usr/include/c++/14/bits/stl_tree.h:2116:42: error: expression cannot be used as a function
 2116 |           __comp = _M_impl._M_key_compare(__k, _S_key(__x));
      |                    ~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/stl_tree.h:2127:33: error: expression cannot be used as a function
 2127 |       if (_M_impl._M_key_compare(_S_key(__j._M_node), __k))
      |           ~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/stl_tree.h: In instantiation of 'std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::iterator std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::_M_insert_(_Base_ptr, _Base_ptr, _Arg&&, _NodeGen&) [with _Arg = const char&; _NodeGen = std::_Rb_tree<char, char, std::_Identity<char>, long long int, std::allocator<char> >::_Alloc_node; _Key = char; _Val = char; _KeyOfValue = std::_Identity<char>; _Compare = long long int; _Alloc = std::allocator<char>; iterator = std::_Rb_tree<char, char, std::_Identity<char>, long long int, std::allocator<char> >::iterator; _Base_ptr = std::_Rb_tree_node_base*]':
/usr/include/c++/14/bits/stl_tree.h:2174:26:   required from 'std::pair<std::_Rb_tree_iterator<_Val>, bool> std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::_M_insert_unique(_Arg&&) [with _Arg = const char&; _Key = char; _Val = char; _KeyOfValue = std::_Identity<char>; _Compare = long long int; _Alloc = std::allocator<char>]'
 2174 |           return _Res(_M_insert_(__res.first, __res.second,
      |                       ~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~
 2175 |                                  _GLIBCXX_FORWARD(_Arg, __v), __an),
      |                                  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/stl_set.h:514:25:   required from '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 = long long int; _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>, long long int, 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]'
  514 |           _M_t._M_insert_unique(__x);
      |           ~~~~~~~~~~~~~~~~~~~~~^~~~~
a.cc:18:19:   required from here
   18 |   rep(i,n)S.insert(s[i]);
      |           ~~~~~~~~^~~~~~
/usr/include/c++/14/bits/stl_tree.h:1824:56: error: expression cannot be used as a function
 1824 |                               || _M_impl._M_key_compare(_KeyOfValue()(__v),
      |                                  ~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~
 1825 |                                                         _S_key(__p)));
      |                                                         ~~~~~~~~~~~~
/usr/include/c++/14/bits/stl_tree.h: In instantiation of 'static const _Key& std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::_S_key(_Const_Link_type) [with _Key = char; _Val = char; _KeyOfValue = std::_Identity<char>; _Compare = long long int; _Alloc = std::allocator<char>; _Const_Link_type = const std::_Rb_tree_node<char>*]':
/usr/include/c++/14/bits/stl_tree.h:2116:47:   required from 'std::pair<std::_Rb_tree_node_base*, std::_Rb_tree_node_base*> std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::_M_get_insert_unique_pos(const key_type&) [with _Key = char; _Val = char; _KeyOfValue = std::_Identity<char>; _Compare = long long int; _Alloc = std::allocator<char>; key_type = char]'
 2116 |           __comp = _M_impl._M_key_compare(__k, _S_key(__x));
      |                                                ~~~~~~^~~~~
/usr/include/c++/14/bits/stl_tree.h:2169:4:   required from 'std::pair<std::_Rb_tree_iterator<_Val>, bool> std::_Rb_tree<_Key, _Val, _KeyOfValue, _Compare, _Alloc>::_M_insert_unique(_Arg&&) [with _Arg = const char&; _Key = char; _Val = char; _KeyOfValue = std::_Identity<char>; _Compare = long long int; _Alloc = std::allocator<char>]'
 2169 |         = _M_get_insert_unique_pos(_KeyOfValue()(__v));
      |           ^~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/stl_set.h:514:25:   required from '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 = long long int; _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>, long long int, 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]'
  514 |           _M_t._M_insert_unique(__x);
      |           ~~~~~~~~~~~~~~~~~~~~~^~~~~
a.cc:18:19:   required from here
   18 |   rep(i,n)S.insert(s[i]);
      |           ~~~~~~~~^~~~~~
/usr/include/c++/14/bits/stl_tree.h:760:23: error: static assertion failed: comparison object must be invocable with two arguments of key type
  760 |         static_assert(__is_invocable<_Compare&, const _Key&, const _Key&>{},
      |                       ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
/usr/include/c++/14/bits/stl_tree.h:760:23: note: 'std::__is_invocable<long long int&, const char&, const char&>()' evaluates to false