source_code: import java.io.PrintWriter;
  import java.util.Scanner;
  
  public class D {
  	
  	public static void main(String [] args){
  		Scanner cin = new Scanner(System.in);
  		PrintWriter cout = new PrintWriter(System.out);
  		long l = cin.nextLong(), r = cin.nextLong(), k = 1;
  		if (l == r)cout.println(0);
  		else {
  			while (((r>>k)<<k)>l)k++;k--;
  			cout.println(((r>>k)<<k)^(((r>>k)<<k)-1));
  		}
  		cout.flush();
  	}
  
  }