#include <bits/stdc++.h>
using namespace std;

int main() {
    long long int a,c;
    cin >> a >>c;
    if(a>c) swap(a,c);
    long long int val = log2(c);
    long long int ans = 1;
    ans <<= val;
    ans = min(--ans, a);
    cout << ans;
    
	// your code goes here

}