#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, x;
	while(cin >> q, q!=-1){
		double x = (double)q/2.0;
		while(1){
			double c = (x*x*x-q);
			double Xn = x-c/(3*x*x);
			x = Xn;
			if(fabs(c) < q*EPS){
				cout.setf(ios::fixed);
				cout.precision(6);
				cout << x << endl;
				break;
			}
		}
	
	}
}