import java.util.*;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        boolean[] used = new boolean[11];
        for (int i = 0; i < 9; i++) {
            used[sc.nextInt()] = true;
        }
        for (int i = 1; i <= 10; i++) {
            if (!used[i]) {
                System.out.println(i);
                return;
            }
        }
    }
}