import java.util.Scanner;

public class Main {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		for(int i=1;i<=9;i++){
			int input = sc.nextInt();
			if(input==i){
				continue;
			}else if(input==9){
				System.out.println(i);
				break;
			}else{
				System.out.println(i);
				break;
			}
		}
		sc.close();
	}// mainmethod

} // class