#include<iostream>
#include<cmath>
using namespace std;
int main() {
	typedef long double ld;
	ld q;
	while (cin >> q) {
		if (q == -1)return 0;
		if (q == 1)cout << "1\n";
		else {
			ld x = q / 2;
			while (abs(x*x*x - q) > 0.00001*q) {
				x = x - ((x*x*x - q) / (3 * x*x));
			}
			printf("%.10f\n", x);
		}
	}
}