#include<bits/stdc++.h>
using namespace std;
using Int = long long;
signed main(){
  Int n;
  cin>>n;
  for(Int i=1;i<n;i++){
    Int x=i,y=n-i;
    if(__builtin_popcountll(x)!=1&&__builtin_popcountll(y)!=1){
      cout<<x<<endl;
      return 0;
    }
  }
  cout<<-1<<endl;
  return 0;
}