import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.math.BigInteger;

public class Main {
	public static void main(String[] args) throws Exception {
		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
		String[] sa = br.readLine().split(" ");
		br.close();

		BigInteger ba = new BigInteger(sa[0]);
		BigInteger bb = new BigInteger(sa[1]);
		System.out.println(ba.xor(bb).toString());
	}
}