package main

import . "fmt"

func main() {
	var a, b int
	Scan(&a,&b)
	Println(solve(a,b))
}
	
func solve(a, b int) int {
	var x, y int
	for i := 62; i >= 0; i-- {
		c := 1 << i
		switch {
			case x+c <= a && y+c <= b:
				if x < y {
					x += c
				} else {
					y += c
				}
			case x+c <= a:
				x += c
			case y+c <= b:
				y += c
		} 
	}
	return min(x,y,x^y)
}

func init() {
	check()
}

func check() {
	for a := 1; a <= 100; a++ {
		for b := 1; b <= 100; b++ {
			s1 := solve(a, b)
			s2 := bruteforce(a, b)
			if s1 != s2 {
				panic(Sprintf("a=%d,b=%d,s1=%d,s2=%d",a,b,s1,s2))
			}
		}
	}
}

func bruteforce(a, b int) int {
	ans := 0
	for x := 0; x <= a; x++ {
		for y := 0; y <= b; y++ {
			ans = max(ans, min(x,y,x^y))
		}
	}
	return ans
}