import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int[] a = new int[9];
		for (int i = 0; i < a.length; i++) {
			a[i] = sc.nextInt();
		}
		for(int i = 0 ; i < 9 ; i++) {
			if (a[i] != i + 1) {
				System.out.println(i);
				return;
			}
		}
	}
}