#pragma GCC optimize("O3,unroll-loops")
#include <bits/stdc++.h>
using namespace std;
typedef int in;
#define int long long
#define double long double
#define f first
#define s second
#define pb push_back
#define pp push
#define ceill(x,y) ((x/y)+(x%y!=0)*(x/abs(x)*y/abs(y)<0?0:1))
#define floorr(x,y) ((x/y)+(x%y!=0)*(x/abs(x)*y/abs(y)<0?-1:0))
#define YN(x) cout<<(x?"YES\n":"NO\n");
#define Yn(x) cout<<(x?"Yes\n":"No\n");
#define yn(x) cout<<(x?"yes\n":"no\n");
const int MAAX=1e18;
const int MOD=1e9+7;
const int MAX=1e9;



in main(){
    ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
    int tc=1;
    // cin>>tc;
    while(tc--){
		int n;
		cin>>n;
		if(__builtin_popcountll(n-1)==1){
			cout<<"1\n";
			return 0;
		}
		for(int i=0;(1ll<<i)<=n;i++){
			if(__builtin_popcountll(n-(1ll<<i)-1)==1){
				cout<<(1ll<<i)+1<<"\n";
				return 0;
			}
		}
		cout<<"impossible\n";
    }
    return 0;
}