Find the MEX with Sets using C++

#include <bits/stdc++.h>

using namespace std;

int main() {
    int n;
    cin >> n;
    set<int> s;
    for (int i = 0; i < n; i++) {
        int x;
        cin >> x;
        s.insert(x);
    }
    int MEX = 1;
    while (s.count(MEX)) {
        MEX++;
    }
    cout << MEX << '\n';
    return 0;
}