#include <bits/stdc++.h>
using namespace std;
using ll=long long;
using ull=unsigned long long;
#define rep(i,n) for(int i=0; i<(n); i++)

ull X;

ull popcount(ull x){
  ull res=0;
  rep(d,63) res += ((x>>d)&1ull);
  return res; 
}

int main(){
  cin>>X;
  for(int d=1; d<=63; d++){
    if(popcount(X^d)==d){ cout<<(X^d)<<"\n"; return 0; }
  }
  cout<<-1<<endl;
  return 0;
}