#include<iostream>
#include<cstdio>
#include<cmath>

using namespace std;

typedef int LL;
typedef double LD;

int main(){

	LL q;
	LD x;

	while(1){

		cin>>q;
		if(q==-1) break;

		x=(LD)q/2.0;
		while(abs(x*x*x-q)>=0.00001*q){
			x=x-(x*x*x-q)/(3.0*x*x);
		}
		printf("%.6lf\n",x);
	}
}