import java.util.Scanner;

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