#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
using namespace std;

int main() {
    int b;
    int ans = 0;
    for(int i = 1;i < 10;i++){
        cin >> b;
        if(b != i){
            ans = i;
            break;
        }
    }
    ans = ans == 0 ? 10 : ans;
    cout << ans << endl;
    return 0;
}