Language: C++

#include<iostream>
#include<string>
#include<cstdio>
#include<cmath>
#include<cstring>
#include<algorithm>
#include<vector>
#include<functional>
#include<iomanip>
#include<queue>
#include<cassert>
#include<tuple>
#include<set>
#include<map>
#include<list>
#include<bitset>

#define PB push_back
#define ALL(a)  (a).begin(),(a).end()
#define all(v) begin(v), end(v)
#define DWN(a)  (a).begin(),(a).end(), greater<int>()
#define rep(i, m) for (int i = 0; i < m; i++)
#define REP(i, n, m) for (int i = n; i < m; i++)

using namespace std;

typedef long long ll;
typedef pair<int, int> P;

const int dx[4] = { 1, 0, -1, 0 };
const int dy[4] = { 0, 1, 0, -1 };
const int INF = (int)1e9;
const ll inf = (ll)1e18;
const ll MOD{ (ll)1e9 + 7 };

int n;
set<int, int> st;

int main()
{
	cin >> n;
	rep(i, n) {
		int a;
		cin >> a;
		st.insert(a);
	}
	int k = st.size();
	if (k % 2) {
		cout << k << endl;
	}
	else {
		cout << k - 1 << endl;
	}
	return 0;
}

Compiler output:
In file included from /usr/include/c++/14/set:62,
                 from a.cc:13:
/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 = int; _Val = int; _KeyOfValue = std::_Identity<int>; _Compare = int; _Alloc = std::allocator<int>; key_type = int]':
/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 int&; _Key = int; _Val = int; _KeyOfValue = std::_Identity<int>; _Compare = int; _Alloc = std::allocator<int>]'
 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 = int; _Compare = int; _Alloc = std::allocator<int>; typename std::_Rb_tree<_Key, _Key, std::_Identity<_Tp>, _Compare, typename __gnu_cxx::__alloc_traits<_Alloc>::rebind<_Key>::other>::const_iterator = std::_Rb_tree<int, int, std::_Identity<int>, int, std::allocator<int> >::const_iterator; typename __gnu_cxx::__alloc_traits<_Alloc>::rebind<_Key>::other = std::allocator<int>; typename __gnu_cxx::__alloc_traits<_Alloc>::rebind<_Key> = __gnu_cxx::__alloc_traits<std::allocator<int>, int>::rebind<int>; typename _Alloc::value_type = int; value_type = int]'
  514 |           _M_t._M_insert_unique(__x);
      |           ~~~~~~~~~~~~~~~~~~~~~^~~~~
a.cc:45:12:   required from here
   45 |                 st.insert(a);
      |                 ~~~~~~~~~^~~
/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 int&; _NodeGen = std::_Rb_tree<int, int, std::_Identity<int>, int, std::allocator<int> >::_Alloc_node; _Key = int; _Val = int; _KeyOfValue = std::_Identity<int>; _Compare = int; _Alloc = std::allocator<int>; iterator = std::_Rb_tree<int, int, std::_Identity<int>, int, std::allocator<int> >::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 int&; _Key = int; _Val = int; _KeyOfValue = std::_Identity<int>; _Compare = int; _Alloc = std::allocator<int>]'
 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 = int; _Compare = int; _Alloc = std::allocator<int>; typename std::_Rb_tree<_Key, _Key, std::_Identity<_Tp>, _Compare, typename __gnu_cxx::__alloc_traits<_Alloc>::rebind<_Key>::other>::const_iterator = std::_Rb_tree<int, int, std::_Identity<int>, int, std::allocator<int> >::const_iterator; typename __gnu_cxx::__alloc_traits<_Alloc>::rebind<_Key>::other = std::allocator<int>; typename __gnu_cxx::__alloc_traits<_Alloc>::rebind<_Key> = __gnu_cxx::__alloc_traits<std::allocator<int>, int>::rebind<int>; typename _Alloc::value_type = int; value_type = int]'
  514 |           _M_t._M_insert_unique(__x);
      |           ~~~~~~~~~~~~~~~~~~~~~^~~~~
a.cc:45:12:   required from here
   45 |                 st.insert(a);
      |                 ~~~~~~~~~^~~
/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 = int; _Val = int; _KeyOfValue = std::_Identity<int>; _Compare = int; _Alloc = std::allocator<int>; _Const_Link_type = const std::_Rb_tree_node<int>*]':
/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 = int; _Val = int; _KeyOfValue = std::_Identity<int>; _Compare = int; _Alloc = std::allocator<int>; key_type = int]'
 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 int&; _Key = int; _Val = int; _KeyOfValue = std::_Identity<int>; _Compare = int; _Alloc = std::allocator<int>]'
 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 = int; _Compare = int; _Alloc = std::allocator<int>; typename std::_Rb_tree<_Key, _Key, std::_Identity<_Tp>, _Compare, typename __gnu_cxx::__alloc_traits<_Alloc>::rebind<_Key>::other>::const_iterator = std::_Rb_tree<int, int, std::_Identity<int>, int, std::allocator<int> >::const_iterator; typename __gnu_cxx::__alloc_traits<_Alloc>::rebind<_Key>::other = std::allocator<int>; typename __gnu_cxx::__alloc_traits<_Alloc>::rebind<_Key> = __gnu_cxx::__alloc_traits<std::allocator<int>, int>::rebind<int>; typename _Alloc::value_type = int; value_type = int]'
  514 |           _M_t._M_insert_unique(__x);
      |           ~~~~~~~~~~~~~~~~~~~~~^~~~~
a.cc:45:12:   required from here
   45 |                 st.insert(a);
      |                 ~~~~~~~~~^~~
/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<int&, const int&, const int&>()' evaluates to false