#include <iostream>
#include <cmath>
#include <cstdio>
using namespace std;
#define EPS 0.00001

//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(1){
			double c = (x*x*x-q);
			x = x-c/(3*x*x);
			
			if(abs(c) < q*EPS){
				printf ("%.6f\n", x);
				//cout.setf(ios::fixed);
				//cout.precision(6);
				//cout << x << endl;
				break;
			}
		}
	
	}
}