#include<iostream>
#include<cmath>
using namespace std;
int main(){
	double x,q;
	
	while(cin>>q){
		if(q==-1)break;
		
		x=q/2;
		
		
		while(fabs( x*x*x-q ) >= 0.00001f * q){
			x = x - (x*x*x-q)/(3*x*x);
		}
		
		cout << x << endl;
	}
}