#include<iostream>
#include<cmath>
using namespace std;
int main() {
	double q;
	while (cin >> q) {
		if (q == -1)return 0;
		double x = q / 2;
		while (abs(x*x*x - q) >= 0.00001*q) 
			x = x - ((x*x*x - q) / (3 * x*x));
		if (q == -1)return 0;
		printf("%.10f\n", x);
	}
}