#include<iostream>
#include<math.h>

using namespace std;

int main(void)
{
	double q;
	while(1){
		cin>>q;
		if(q==-1) break;
		double x=q/2;
		while(1){
			x=x-((x*x*x-q)/(3*x*x));
			if(abs(x*x*x-q)<0.00001*q) break;
		}
		cout<<x<<endl;
	}
	return 0;
}