#include <iostream>
#include <cstdio>

using namespace std;
#define rep2(x,from,to) for(int x = (from); x < (to); ++(x))
#define rep(x,to) rep2(x,0,to)
int main() {
	double q;
	while(cin >> q && q != -1) {
		double x = q/2;
		while(x*x*x-q>=0.00001*q) {
			x = x - (x*x*x-q)/(3*x*x);
		}
		printf("%.6lf\n", x);
	}
	return 0;
}