package main

import "fmt"

func main() {
    // Based on http://www.kaoriya.net/blog/2013/02/04/
	var a, b, c int
	fmt.Scan(&a, &b)
	for b != 0 {
		c = (a & b) << 1
		a ^= b
		b = c
	}
	fmt.Println(a)
}