#include <stdio.h>
#include <stdbool.h>

int main(void)
{
  bool isFound = false;
  int num;
  int check_num = 0;

  while (~scanf("%d", &num))
  {
    check_num++;
    if (num != check_num) {
      printf("%d\n", check_num);
      isFound = true;
      break;
    }
  }
  if (isFound == false) {
    check_num++;
    printf("%d\n", check_num);
  }  
  return 0;
}