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

int main() {
  int A, B; cin >> A >> B;
  int mx = 0;
  for (int x = 0; x < A; ++x) {
    for (int y = 0; y < B; ++y) {
      int mn = min(A, min(B, A ^ B));
      if (mn > mx) mx = mn;
    }
  }
  cout << mx << endl;
}