#include <bits/stdc++.h>
#define rep(i,l,n) for(int i=l;i<n;i++)
#define rer(i,l,n) for(int i=l;i<=n;i++)
#define all(a) a.begin(),a.end()
#define o(a) cout<<a<<endl
#define fi first
#define se second
using namespace std;
typedef long long ll;
typedef vector<int> vint;
typedef pair<int,int> pii;

int main(){
	int q;
	while(1){
		cin>>q;
		if(q==-1) break;
		double x=(double)q/2;
		while(1){
			x=x-(double)(x*x*x-q)/(3*x*x);
			if(abs(x*x*x-q)<1e-5*q) break;
		}
		printf("%.7lf\n",x);
	}
}