import java.util.Scanner;

public class Main {

	public static void main(String[] args) {
		Scanner sc = new Scanner(System.in);
		long a = sc.nextLong();
		long c = sc.nextLong();
		System.out.println(a ^ c);
 	}
}
// a ^ b = c
// a ^ b ^ b = a // c ^ b = a
// b ^ c ^ c = b // a ^ c = b