import java.util.*;

public class Main{
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    for(int i=1;i<10;i++){
      if(sc.nextInt() != i){
        System.out.println(i);
        break;
      }
      if(i==9)System.out.println("10");
    }
  }
}