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

int main(){
	double q, x;
	while(std::cin >> q, q != -1){
		x = q/2;
		while(fabs(x*x*x-q) >= 0.00001*q){
			x = x - (x*x*x-q) / (3*x*x);
		}
		printf("%.6lf\n", x);
	}
}