#include <bits/stdc++.h>
using namespace std;

constexpr double EPS = 0.00001;

int main() {
	cout.precision(10);
	cout.setf(ios::fixed);

	for(int q; cin >> q && q != -1;) {
		double x = q / 2.0;

		while(abs(x * x * x - q) >= EPS * q) {
			x -= ((x * x * x) - q) / (3 * x * x);
		}

		cout << x << endl;
	}

	return EXIT_SUCCESS;
}