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


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