#include<iostream>
#include<iomanip>
#include<cmath>
using namespace std;

int main()
{
	double a, q;
	cout<<setprecision(6);
	cout<<setiosflags(ios::fixed);
	while (cin>>q, q!=-1) {
		a = q/2.0;
		while ( abs(a*a*a-q) >= 0.00001*q ) a -= (a*a*a-q) / (3.0*a*a);
		cout<<a<<endl;
	}
	return 0;
}