import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class No581 {
	public static void main(String[] args) throws IOException{
		String[] str = new BufferedReader(new InputStreamReader(System.in)).readLine().split(" ");
		long a = Long.parseLong(str[0]);
		long c = Long.parseLong(str[1]);
		System.out.println(a^c);
	}
}