import java.io.*;

import java.util.*;

import java.text.*;

import java.math.*;

import java.util.regex.*;

public class Solution {

/*

* Complete the function below.

*/

static int maxXor(int l, int r) {

int res=-1;

for(int a=l;a<=r;a++){

for(int b=a;b<=r;b++){

if((a^b)>res){

res=a^b;

}

}

}

return res;

}

public static void main(String[] args) {

Scanner in = new Scanner(System.in);

int res;

int _l;

_l = Integer.parseInt(in.nextLine());

int _r;

_r = Integer.parseInt(in.nextLine());

res = maxXor(_l, _r);

System.out.println(res);

in.close();

}

}