#include<bits/stdc++.h>
using namespace std;
using ll=long long;
int main(){
  ll X; cin>>X;
  if(__builtin_popcountll(X^1)==1){
    cout<<(X^1)<<endl;
    return 0;
  }
  if(__builtin_popcountll(X^2)==2){
    cout<<(X^2)<<endl;
    return 0;
  }
  for(ll M=1,two=1;two<=X;M++,two*=2){
    if(__builtin_popcountll(X^M)==M){
      cout<<(X^M)<<endl;
      return 0;
    }
  }
  puts("-1");
}