#include<bits//stdc++.h>
using namespace std;
int main(){
	int a;
	while(cin>>a&&a!=-1){
		double x1=a/2,x2;
		int i=1;
		if(a==1){
			cout<<"1.00000"<<endl;
		}
		else{
			while(true){  
				x2=x1-(x1*x1*x1-a)/(3*x1*x1);
				if(abs(x2*x2*x2-a)<0.00001*a) 
				{
					cout<<x2<<endl;
					break;
				}
				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;
}