#include<bits/stdc++.h>
using namespace std;
#define ERROR ios::sync_with_stdio(0); cin.tie(0); cout.tie(0); fileIO();
typedef long long ll;
typedef unsigned long long ull;
typedef long double ld;
void fileIO(){
    #ifndef ONLINE_JUDGE
    freopen("io\\input.txt", "r", stdin);
    freopen("io\\output.txt", "w", stdout);
    #endif
}

const ll mod = 1e9 + 7, N = 2e5 + 5;

void TestCase() {
    int n;
    cin >> n;
    string s;
    cin >> s;
    bool vis[n + 1] = {};
    int currentsubstr = 1;
    int cnt = 0;
    for(int i = 0; i < n;)
    {
        string current = s.substr(i, currentsubstr);
        if(currentsubstr == 1 || i == n - 1)
            vis[s[i] - '0' ] = true;
        else 
            vis[(s[i] - '0') * 10 + s[i + 1] - '0'] = true;

        if(i > 0 && s[i] - 1!= s[i - 1])
            cnt += 2;
        else
            cnt++;

        if(cnt <= 9)
            i++;
        else
            i += 2;

        if(cnt >= 9)
        currentsubstr++;
    }
    for(int i = 1; i <= n; i++)
    {
        if(!vis[i])
        {
            cout << i << '\n';
            return;
        }
    }
    
}

int main() {
    
    ERROR;

    int t = 1;
    //cin >> t;

    while(t--)
        TestCase();

}