#include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define repr(i, n) for (int i = (int)(n); i >= 0; i--)
#define all(v) v.begin(), v.end()
#define mod1 1000000007
#define mod2 998244353
typedef long long ll;

int main(){
    ll A,B;
    cin >> A >> B;
    if (A > B) swap(A, B);
    ll allow_min = A;
    if (A == B) allow_min--;

    ll ans = 0;
    ll x = 1;
    while(true){
        if (x - 1 > allow_min){
            break;
        }
        ans = max(ans, x - 1);
        x *= 2;
    }
    if (ans < (A ^ B)) ans = max(ans, A);
    cout << ans << endl;
}