#include <stdio.h>
int main() {
  int B[9] = {'\0'}, i;
  for (i = 0; i < 9; i++) {
    scanf("%d", &B[i]);
    if (i+1 != B[i]) {
      printf("%d\n", i+1);
      break;
    }
  }
  return 0;
}