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

int main() {
    int r = 10;
    for (int i = 1; i < 10; i++) {
        int b;
        cin >> b;
        if (i != b) {
            r = i;
            break;
        }
    }
    cout << r << endl;

    return 0;
}