lec-A[18]

#include <bits/stdc++.h>

using namespace std;

#define all(x) x.begin(), x.end()

int mex(vector<int> a) {
    int n = a.size();
    sort(all(a));
    if (a[0] > 0) {
        return 0;
    }
    for (int i = 0; i < n - 1; ++i){
        if (a[i] + 1 < a[i + 1]){
            return a[i] + 1;
        }
    }
    return a.back() + 1;
}

int main() {
    int n;
    cin >> n;
    vector<int> a(n);
    for (int i = 0; i < n; ++i){
        cin >> a[i];
    }
    cout << mex(a) << endl;
}