#include <iostream>
#include <cmath>
using namespace std;
#define EPS 1e-5

//0080
int main(){
	// x^3=qを漸化式でとく
	// X(n+1) = X(n)-( X(n)^3 - q )/( 3*(X(n)^2) )

	int q;
	while(cin >> q, q!=-1){
		double x = (double)q/2.0;
		while(fabs(x*x*x-q) >= q*EPS){
			x = x - (x*x*x-q)/(3*x*x);
		}

		cout.setf(ios::fixed);
		cout.precision(6);
		cout << x << endl;
	}
	return 0;
}