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

public class No00000581_Main {
	static BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
	public static void main(String[] args) throws IOException {
		String[] t = br.readLine().split(" ");
		String a = Long.toBinaryString(Long.parseLong(t[0]));
		String c = Long.toBinaryString(Long.parseLong(t[1]));
		int len = Math.max(a.length(), c.length());
		a = String.format("%" + len + "s", a).replaceAll(" ", "0");
		c = String.format("%" + len + "s", c).replaceAll(" ", "0");
		char[] b = new char[len];
		for(int i = 0; i < a.length(); i++) {
			if(a.charAt(i) == c.charAt(i)) {
				b[i] = '0';
			} else {
				b[i] = '1';
			}
		}
		System.out.println(Long.parseLong(new String(b), 2));
	}
}