#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 = 1;i <= n;i++) {
		string cur = to_string(i);
		int sz = cur.size();
		bool found = false;
		for(int j = 0;j + sz <= s.size();j++) {
			bool ok = true;
			for(int k = j;k < j + sz;k++)
				ok &= (!done[k]);
			if(!ok)
				continue;
			string tmp = s.substr(j, sz);
			if(tmp == cur) {
				for(int k = j;k < j + sz;k++)
					done[k] = true;
				found = true;
				break;
			}
		}
		if(!found)
			return cout << i, 0;
	}
    return 0;
}