#include <iostream>
#include <cmath>
#include <cstdio>
using namespace std;

int main() {
	double q;
	while (cin >> q, q >= 0.0) {
		double x = q / 2.;
		while (fabs(x * x * x - q) >= 0.00001 * q) {
			x = x - (x * x * x - q) / (3 * x * x);
		}
		printf("%.6lf\n", x);
	}
	return 0;
}