//#include <atcoder/all>
#include <iostream>
#include <numeric>
#include <cmath>
#include <limits>
#include <stdio.h>
#include <iomanip>
#include <string> // string, to_string, stoi
#include <vector> // vector
#include <algorithm> // min, max, swap, sort, reverse, lower_bound, upper_bound
#include <utility> // pair, make_pair
#include <tuple> // tuple, make_tuple
#include <cstdint> // int64_t, int*_t
#include <cstdio> // printf
#include <map> // map
#include <queue> // queue, priority_queue
#include <set> // set
#include <stack> // stack
#include <deque> // deque
#include <unordered_map> // unordered_map
#include <unordered_set> // unordered_set
#include <bitset> // bitset
#include <cctype> // isupper, islower, isdigit, toupper, tolower
using namespace std;
//using namespace atcoder;
using ll = long long;
#define all(A) A.begin(),A.end()
using vll = vector<ll>;
#define rep(i, n) for (long long i = 0; i < (long long)(n); i++)
using Graph = vector<vector<pair<ll,double>>>;

vector<pair<ll,ll>> Z;
double dist(ll A,ll B){
    ll dx=Z[A].first-Z[B].first;
    ll dy=Z[A].second-Z[B].second;
    return sqrt(dx*dx+dy*dy);
}

ll mod=1e9+7;
int main() {
   ll X;
   cin>>X;
   rep(i,70){
       ll Y=X^i;
       ll k=0;
       rep(p,70){
           k+=Y%2;
           Y/=2;
       }
       if(k==i){
           cout<<(X^k)<<endl;
           return 0;
       }
   }
  cout<<-1<<endl;
}