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

int main() {
	while (1) {
		long long q;
		double x;
		cin >> q;
		if (q == -1) break;
		x = (double)q / 2;
		while (fabs(x*x*x - q) >= 1e-5*q) {
			x = x - (x*x*x - q) / (3 * x*x);
		}
		printf("%.6f\n", x);
	}
}
