#include <bits/stdc++.h>
using namespace std;
typedef long long ll;

int main() {
    ll x;
    cin >> x;
    if (x == 1) {
        cout << "1\n";
        return 0;
    }
    x = (x + 1) / 2 + 1;
    vector<int> f;
    set<ll> s;
    f.push_back(1);
    f.push_back(2);
    s.insert(1);
    s.insert(2);
    while (*f.rbegin() * 2 - 1 <= x)
        f.push_back(*f.rbegin() * 2 - 1), s.insert(*f.rbegin());
    for (ll xx : f)
        if (s.find(x - xx) != s.end()) {
            cout << xx * 2 - 1 << '\n';
            return 0;
        }
    cout << "impossible\n";
    return 0;
}