import java.util.Scanner;

public class No481 {
	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		int t[] = new int[9];
		int i;
		
		for(i = 0;i < 9;i++) {
			t[i] = sc.nextInt();
		}
		
		for(i = 1;i <= 9;i++) {
			if(t[i - 1] != i) {
				break;
			}
		}
		
		System.out.println(i);
	}
}