#include <iostream>
using namespace std;

int main() {
  // 入力
  int a[9];
  for (int i = 0; i < 9; i++) cin >> a[i];

  int ans = -1;
  for (int i = 0; i < 8; i++) {
    if (a[i+1] - a[i] == 2) ans = i + 2;
  }

  // 解答
  cout << (ans == -1 ? 10 : ans) << endl;

  return 0;
}