abc245_b_mex.cpp

// Mex | https://atcoder.jp/contests/abc245/tasks/abc245_b
// Time: O(n+2001); extra space: O(2001).
#include <algorithm>
#include <iostream>
#include <string>
#include <vector>

void solve() {
    int n;
    std::cin>>n;
    std::vector<bool>present(2002);
    while(n--) {
        int x;
        std::cin>>x;
        present[x]=true;
    }
    int answer=0;
    while(present[answer])++answer;
    std::cout<<answer<<'\n';
}

int main() {
    std::ios::sync_with_stdio(false);
    std::cin.tie(nullptr);
    solve();
}