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();     
        
       
    }
}