package yukicoder;

import java.util.Scanner;

public class N481 {
	public static void main(String[] args){
		Scanner sc = new Scanner(System.in);
		int i;
		for(i = 1;i <= 9;++i){
			if(sc.nextInt() != i){
				System.out.println(i);
				return;
			}
		}
		System.out.println(10);
	}
}