#include <iostream>
#include <queue>
#include <stack>
#include <vector>
#include <stdio.h>
#include <algorithm>
#include <string.h>
#include <string>
#include <cmath>
#include <complex>
#include <map>
using namespace std;

#define rep(i,n) for(int i=0;i<int(n);++i)
#define ALL(v) (v).begin(),(v).end()
#define PB push_back
#define EPS 1e-5
#define F first
#define S second

static const double PI=6*asin(0.5);
typedef pair<double,double> P;
typedef complex<double> CP;
typedef long long ll;

double x;
ll q;
int main(){
	while(cin>>q,q!=-1){
		x=q/2.0;
		while(abs(x*x*x-q)>=EPS*q){
			x-=(x*x*x-q)/3.0/x/x;
		}
		printf("%.6f\n",x);
		
	}
		
	return 0;
}