#include<iostream>
#include<cstdio>
using namespace std;
int main(){
	double x,p;
	while(cin>>p,p!=-1){
		x=p/2;
		while(max(x*x*x-p,p-x*x*x)>=0.00001*p){
			x=x-(x*x*x-p)/(3*x*x);
		}
		printf("%.6lf\n",x);
	}
	return 0;
}
	
	