import java.util.Scanner;

public class A000481 {

	public static void main(String[] args) {
		Scanner s = new Scanner(System.in);
		for(int i=0;i<9;i++) {
			if(s.nextInt()-i!=1) {
				System.out.println(i+1);
				break;
			}
			if(i==8)System.out.println(10);
		}
		s.close();
	}
}