package yukikoda;
import java.util.Scanner;
public class no481 {
	public static void main(String[] args) {
		int[] num = new int[9];
		int number = 10;
		Scanner sc = new Scanner(System.in);

		for(int i=0; i<9; i++) {
			num[i] = sc.nextInt();
		}

		for(int j=1; j<=9; j++) {
			if(num[j-1] != j) {
				number = j;
				break;
			}
		}

		System.out.println(number);
	}
}