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(" ");
		int a = Integer.parseInt(str[0]);
		int c = Integer.parseInt(str[1]);
		System.out.println(a^c);
	}
}