#include <bits/stdc++.h>

using namespace std;

int main() {
    vector<int> b(9);
    for (int i = 0; i < 9; i++) {
        cin >> b.at(i);
    }
    if (b.at(0) == 2) {
        cout << 1 << endl;
        return 0;
    }
    if (b.at(8) == 9) {
        cout << 10 << endl;
        return 0;
    }
    for (int i = 1; i < 9; i++) {
        if (b.at(i) == b.at(i - 1) + 1) {
            continue;
        } else {
            cout << i + 1 << endl;
            break;
        }
    }
    return 0;
}