import java.util.*;

public class Main {
	public static void main(String args[]) {
		Scanner scan = new Scanner(System.in);

		int a = scan.hasNextInt() ? scan.nextInt() : -1;
		int b = scan.hasNextInt() ? scan.nextInt() : -1;
		if (a > 1000 || a < 0 || b > 1000 || b < 1) {
			System.out.println("入力エラー");
			return;
		}

		int ans = (a | b) - (a & b);

		// 結果出力
		System.out.println(ans);

	}
}