#include<bits//stdc++.h>
using namespace std;
int main(){
	int a;
	while(true){
		cin>>a;
		if(a==-1) {break;}
		double x1=a/2,x2;
		int i=1;
		while(true){
			if(i%2==1){
				x2=x1-(x1*x1*x1-a)/(3*x1*x1);
				if(abs(x2*x2*x2-a)<0.00001*a) 
				{
					cout<<x2<<endl;
					break;
				}
			}
			else{
				x1=x2-(x2*x2*x2-a)/(3*x2*x2);
				if(abs(x1*x1*x1-a)<0.00001*a) 
				{
					cout<<x1<<endl;
					break;
				}
			}
			i++;
		}

	}
	return 0;
}