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


int main(){
	int q;
	while(cin>>q&&~q){
		double x=q/2.;
		while(1e-5*q <= fabs(x*x*x-q)){
			x = x-(x*x*x-q)/(3*x*x);
		}
		printf("%.8f\n",x);
	}
	return 0;
}