#include <iostream>
#include <vector>
#include <algorithm>
#include <fstream>
#include <cmath>

using namespace std;

int main(){

	int q;
	while(cin>>q&&q!=-1){
		double x=(double)q/2;
		while(abs(x*x*x-q)>=0.00001*q){
			x = x - (x*x*x-q)/(3*x*x);
		}
		printf("%.10f\n",x);
	}

	return 0;
}