#include<cstdio>
using namespace std;
int main(void)
{
	int qq;
	double q,x1,x2,xx;
	while(1)	{
		scanf("%d",&qq);
		if(qq==-1)	break;
		q=double(qq);
		x1=q/2.0;
		while(1)	{
			xx=x1*x1*x1-q;
			if(xx<0)	xx=-xx;
			if(xx<0.00001*q)	break;
			x1=x1-(x1*x1*x1-q)/(3.0*x1*x1);
		}
		printf("%lf\n",x1);
	}
	return 0;
}
