#include <bits/stdc++.h>
using namespace std;
int main()
{
    int a,b;
    cin>>a>>b;
    int A=0,c;
    int i=a;
    while(i<=b)
    {
        int j=a++;
        while(j<=b)
        {
           c=i^j;
            A=max(A,c);
            j++;
        }
        i++;
    }
    cout<<A;
}