//1から10

#include <iostream>

using namespace std;

int b[9];

int main() {
    int i;
    bool NotTen = false;
    for(i = 0; i < 9; i++) {
        cin >> b[i];
        if(b[i] != i + 1) {
            NotTen = true;
            break;
        }
    }
    if(NotTen == true) cout << i + 1 << endl;
    else cout << 10 << endl;

    return 0;    
}