#include <iostream>
#include <cmath>
#include <cstdio>

using namespace std;

int main() {
	long double q;
	while (cin >> q) {
		if (q == (long double)-1.0) {
			break;
		}
		long double x = q / (long double)2.0;
		x = x - (((q*q)-(long double)1.0)/((long double)16.0*x*x))*q;
		while (fabs(x*x*x-q) >= 0.00001*q) {
			x = x - (x*x*x-q)/((long double)3.0*x*x);
		}
		printf("%.6lf\n", x);
	}
	return 0;
}