#include <bits/stdc++.h>
using namespace std;
#define int long long
map<int,int>hm;
signed main(){
    cin.tie(nullptr)->sync_with_stdio(false);
    int n;
    cin >> n;
    {
        hm[1] = 1;
        int i = 3;
        while(i < (int)2e18){
            hm[i] = 1;
            i*=2;
            i--;
        }
    }
    if(hm[n]){
        cout << "1\n";
        return 0;
    }
    int i = 3;
    while(i <= n){
        if(!hm[n-i+1]){
            i*=2; i--;
        }
        else{
            cout << i << '\n';
            return 0;
        }
    }
    cout << "impossible\n";
    return 0;
}