#pragma GCC optimize ("O3")
#pragma GCC optimize ("unroll-loops")
//#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
#include <bits/stdc++.h>
typedef long long ll;
typedef long double ld;
using namespace std;
const int N = 1e5 + 5;
int n;
string s;
bool done[N];
int main() {
    ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
    cin >> n >> s;
    for(int i = 0;i < s.size();i++) {
		int cur = s[i] - '0';
		if(!done[cur]) {
			done[cur] = true;
		} else {
			cur *= 10;
			i++;
			cur += s[i] - '0';
			if(!done[cur])
				done[cur] = true;
			else {
				cur *= 10;
				i++;
				cur += s[i] - '0';
				done[cur] = true;
			}
		}
	}
	for(int i = 1;i <= n;i++)
		if(!done[i])
			return cout << i, 0;
    return 0;
}