#include <bits/stdc++.h>

using namespace std;

int main() {
  int ans = -1;
  for (int i = 1; i < 10; ++i) {
    int b;
    cin >> b;
    if (b != i && ans == -1) {
      ans = i;
    }
  }
  cout << (ans > 0? ans: 10) << '\n';
  return 0;
}