#include <bits/stdc++.h>

using namespace std;

int main(void) {
  vector<int> b(9);
  for (int i = 0; i < 9; i++) {
    cin >> b[i];
  }

  bool ten = true;
  for (int i = 0; i < 9; i++) {
    if (b[i] == i + 1) continue;
    cout << i + 1 << endl;
    ten = false;
    break;
  }
  if (ten) {
    cout << 10 << endl;
  }

  return 0;
}