#include <bits/stdc++.h>
using namespace std;
using ll=long long;
using ld=long double;
ll inf=10010010010010010;
ll mod=1000000007;
int main(){
    ll a,b;
    cin >> a >> b ;
    ll x=min(a,b);
    ll y=max(a,b);
    while (1)
    {
        x/=2;
        y/=2;
        if (x==0)
        {
            if (y!=0)
            {
                cout << min(a,b) << endl;
                return 0;
            }
            break;
        }
    }
    
    x=1;
    while (x<a&&x<b)
    {
        x*=2;
    }
    if (x==a||x==b)
    {
        if (a==b)
        {
            cout << x-1 << endl;
        }else if (max(a,b)>=x*2)
        {
            cout << x << endl;
        }else{
            cout << x-1 << endl;
        }
    }else{
        if (x-1==min(a,b)&&b!=a)
        {
            cout << x-1 << endl;
            return 0;
        }
        x/=2;
        x-=1;
        cout << x << endl;
    }
    
}