#include <iostream>
#include <stdio.h>
#include <math.h>
using namespace std;


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