#include<iostream>
#include<cstdio>
#include<cmath>
using namespace std;
int main()
{
	int q;
	while(cin>>q,q!=-1) 
	{
		double x=q/2;
		while(abs(x*x*x-q)>=0.00001*q)
		{
			x=x-(x*x*x-q)/(3*x*x);
		}
		printf("%lf\n",x);
	}
  return 0;
}