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

int main() {
    cin.tie(0);
    ios_base::sync_with_stdio(false);
    
    ll x;
    cin >> x;
    rep(i, 64) {
        if (i == __builtin_popcount(x ^ i)) {
            cout << (x ^ i) << endl;
            return 0;
        }
    }
    cout << -1 << endl;
    return 0;
}