#include<bits/stdc++.h>
#define rep(i,n)for(int i=0;i<n;i++)
#define EPS 1e-5
using namespace std;

int main() {
	double q;
	while (cin >> q, q != -1.) {
		double x = q / 2;
		while (abs(x*x*x - q) >= EPS*q) {
			x -= (x*x*x - q) / (3 * x*x);
		}
		printf("%6lf\n", x);
	}
}