#include <iostream>
#include <cmath>
#include <iomanip>
using namespace std;
double ZKS(double x,double q){
	return (x - ((x * x * x) - q) / (3 * x * x));
}

int main(void){
	double q;

	while(cin >> q){
		if(q == -1) break;

		double x1 = q / 2;
		double x = x1;

		while(abs(x * x * x - q) > 0.00001 * q){
			x = ZKS(x,q);
		}

		cout << fixed;
		cout << setprecision(6) << x <<endl;
	}

	return 0;
}
