#include <bits/stdc++.h>

#define ll long long
using namespace std;

const int N = 2e2 + 5, M = 15;


void tc() {
    ll n;
    cin >> n;
    if (__builtin_popcountll(n) < 4) {
        ll pos = n / 2;
        if (pos % 2 == 0)
            pos++;
        cout << pos << '\n';
    } else cout << "impossible";
}

signed main() {
    ios::sync_with_stdio(0), cin.tie(0), cout.tie(0);
    int t = 1;

//    cin >> t;

    while (t--) {
        tc();
    }

    return 0;
}