#include <iostream>
#include <cmath>
#include <cstdio>
using namespace std;
int main(void){
	int a;
	while(cin>>a){
		if(a==-1)break;
		double q = (double)a;
		double x = q/2;
		while(abs(x*x*x-q)>=0.00001*q){
			double nx = x-(x*x*x-q)/(3*x*x);
			x = nx;
		}
		printf("%.6lf\n",x);
	}
	return 0;
}