// Hey there.. I love you <3
#include <bits/stdc++.h>

using namespace std;
using ll = long long;

mt19937 rnd(time(nullptr));

const int N = 1e5 + 5, mod = 1e9 + 7;
const double pi = acos(-1), eps = 1e-10;


void work() {
    
    ll x;
    cin >> x;
    --x;
    int b = __builtin_popcountll(x);
    if (b > 2)
        cout << "impossible" << endl;
    else
        cout << (x & -x) + 1 << endl;
    
    
    
}


void init() {
    cin.tie(nullptr);
    istream::sync_with_stdio(false);
//    freopen("in.txt", "r", stdin);
//    freopen("out.txt", "w", stdout);


}

int main() {
    init();
    
    int testCases = 1;
//    cin >> testCases;
    while (testCases--) work();
    
    return 0;
}