#include <bits/stdc++.h>

#define sz(x)  (int)x.size()
#define bigint __int128
#define el '\n'
#define ll long long
using namespace std;

void acc() {
    int n;
    cin >> n;
    string s;
    cin >> s;
    int idx = -1;
    for (int i = 1; i <= n; i++) {
        string t = to_string(i);
        if (s.find(t) == string::npos) {
            idx = i;
            break;
        }
    }
    cout << idx << el;

}

int main() {
    cout.tie(0);
    cin.tie(0);
    ios_base::sync_with_stdio(0);
    int t = 1;
    // cin >> t;
    while (t--)acc();
}