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);
                System.exit(1);
            }

        }
        System.out.println(10);
    }
}