#include <stdio.h>

int main(void){
  int b[11],check = 1;
  for(int i = 1; i < 10; i++){
    scanf("%d",&b[i]);
    if(b[i] != i){
      printf("%d\n",i);
      check = 0;
      break;
    }
  }
  if(check == 1)printf("%d\n",10);
  return 0;
}