#include <algorithm>
#include <cmath>
#include <cstdio>
#include <functional>
#include <iomanip>
#include <iostream>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <stack>
#include <string>
#include <vector>
using namespace std;
using ll = long long;
int main() {
  ll a, b;
  cin >> a >> b;
  ll c = max(a, b);
  ll d = min(a, b);
  if(c == 1) {
    cout << 0 << endl;
    return 0;
  }
  ll ans = 1;
  while(ans * 2 - 1 <= d) {
    ans *= 2;
  }
  if(c == d) {
    ans /= 2;
  }
  cout << ans - 1 << endl;
  return 0;
}