import java.util.*;

public class Main {
	static Scanner sc = new Scanner(System.in);
	public static void main(String[] args) {
		int[] ar = new int[11];
		ar[0]++;
		for (int i=0; i<9; i++) {
			ar[sc.nextInt()]++;
		}
		for (int i=0; i<ar.length; i++) {
			if (ar[i]==0) {System.out.println(i);}
		}
	}
}