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

int main() {
	double q, x;
	while (cin >> q&&q!=-1) {
		x = q / 2;
		while (abs((x*x*x) - q) > 0.00001*q) {
		x=x - (((x*x*x) - q) / (3 * x*x));
		}
		cout << fixed << setprecision(7) << x << endl;
	}
	return 0;
}