/// tban lecodes el bosta2
#pragma GCC optimize("O3")
#pragma GCC optimize ("unroll-loops")
#pragma GCC target("avx,avx2,fma")
#include "bits/stdc++.h"
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>

using namespace std;
using namespace __gnu_pbds;


#define pb push_back
#define F first
#define S second
#define f(i, a, b)  for(int i = a; i < b; i++)
#define all(a)  a.begin(),a.end()
#define rall(a) a.rbegin(),a.rend()
#define sz(x) (int)(x).size()
#define mp(x,y) make_pair(x,y)
#define popCnt(x) (__builtin_popcountll(x))
#define int ll

using ll = long long;
using ii = pair<int, int>;
using ull = unsigned long long;
const int N = 2e5+5, LG = 18, MOD = 1e9+7;
const long double PI = acos(-1);
const long double EPS = 1e-7;

const string TARGET = "WALDO";

bool check(ll x) {return x & (x-1);}

void doWork() {

    ll n;
    cin >> n;

    for(int p = 1; p <= n; p *= 2) {
        if(!check(n-p-1)) {
            cout << p + 1 << '\n';
            return;
        }
    }

    cout << "impossible\n";


}
int32_t main() {
#ifdef ONLINE_JUDGE
    ios_base::sync_with_stdio(0);
    cin.tie(0);
#endif // ONLINE_JUDGE

    int t = 1;
//    cin >> t;
    while (t--) {
        doWork();
    }
    return 0;
}