#include <bits/stdc++.h>
using namespace std;
int main(){
  long long X;
  cin >> X;
  long long N = -1;
  for (int i = 0; i < 62; i++){
    if (__builtin_popcountll(X ^ i) == i){
      if (1 <= (X ^ i)){
        N = X ^ i;
      }
    }
  }
  cout << N << endl;
}