#include <bits/stdc++.h>
#define fi first
#define se second
#define pb push_back
#define all(x) (x).begin(),(x).end()
#define SZ(x) ((int)x.size())
#define rep(i,a,n) for(int i=a;i<n;i++)
#define per(i,a,n) for(int i=n-1;i>=a;i--)
#define IOS ios::sync_with_stdio(0);cin.tie(0);cout.tie(0);
using namespace std;
using ll = long long;
using PII = pair<int,int>;
using db = double;
using ull = unsigned long long;
mt19937 mrand(random_device{}());
const int N = 100010, M = 18;


int main(){    
    IOS
    ll n;cin >> n;
    ll m = n;
    if (n <= 3) {
        cout << (n + 1) / 2 << endl;
        return 0;
    }
    n--;
    int cnt = __builtin_ctzll(n);
    n >>= cnt;
    ll ans = 0;
    if (n == 1){
        ans = (1ll << (cnt - 1)) + 1;
    }
    else{
        n--;
        int cnt2 = __builtin_ctzll(n);
        n >>= cnt2;
        if (n != 1){
            cout << "impossible\n";
            return 0;
        }
        ans = (1ll << cnt) + 1;
    }
    cout << ans << endl;
    return 0;
}