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

using namespace std;

typedef long long LL;
typedef long double LB;

int main(){

	LL q;
	LB x;

	while(1){

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

		x=(LB)q/2;
		while(abs(x*x*x-q)>=0.00001*q){
			x=x-(x*x*x-q)/(3*x*x);
		}
		printf("%.6f\n",x);
	}
}