#include <cstdio>
#include <cmath>
using namespace std;

int main()
{
	double q,x;
	while(scanf("%lf",&q), q!=-1)
	{
		x=q/2.0;
		while(abs(x*x*x-q) >= 0.00001*q)
		{
			x = x-(x*x*x-q)/(3*x*x);
		}
		printf("%.6lf\n",x);
	}
}