#include <bits/stdc++.h>
using namespace std;

int main() {
  int b;

  for (int i = 0; i < 9; i++) {
    cin >> b;
    if (b != i + 1) {
      cout << i + 1 << endl;
      break;
    }
    if (i == 8) {
      cout << "10" << endl;
    }
  }
}