#include <bits/stdc++.h>
using namespace std;

typedef long long ll  ;

const int N = 1e5 + 10;

int main() {
    cin.tie(0);cin.sync_with_stdio(0);
    cout.tie(0);cout.sync_with_stdio(0);
    int n; cin >> n;
    string s; cin >> s;
    for (int i = 0, j = 1; j <= n; ++j) {
        int x = j, sz = 0;
        while (x) {
            x /= 10;
            sz++;
        }
        if (stoi(s.substr(i, sz)) != j) {
            cout << j;
            return 0;
        }
        i += sz;
    }
}