#include <bits/stdc++.h>

using namespace std;

int main() {
    int num = 0;
    int tmp;
    for (int i = 1; i <= 9; i++) {
        cin >> tmp;
        if (i != tmp) {
            num = i;
            break;
        }
    }
    
    if (num == 0) {
        cout << 10 << endl;
    } else {
        cout << num << endl;
    }
    
    return 0;
}