#include <iostream>
#include <stdio.h>
#include <math.h>

using namespace std;

int main(){
	int q;
	double xn1,xn;

	while(cin>>q){
		if(q==-1)break;
		xn = q/2.0;
		while(true){
			xn1 = xn - ( (xn*xn*xn - q)/(double)(3*xn*xn) );
			if(fabs(xn1*xn1*xn1 - q)<=0.00001*q){
				break;
			}
			xn = xn1;
		}
		printf("%.6f\n",xn1);
	}
	return 0;
}

/*
Sample Input
15
15
-1
Output for the Sample Input
2.466212
2.466212
*/