#include<iostream>
#include<cmath>
#include<iomanip>
#include<algorithm>
using namespace std;

int main() {
	double q;
	while (true) {
		cin >> q;
		if (q == -1) {
			break;
		}
		double x_p;
		double x_n = q / 2;
		double limit = 0.00001 * q;
		while (abs(x_n * x_n * x_n - q) >= limit) {
			x_p = x_n;
			x_n = x_p - (x_p * x_p * x_p - q) / (3 * x_p * x_p);

		}
		cout << fixed << setprecision(6) << x_n << endl;
			
		
	}
	return 0;
}
