#include <iostream>
#include <cmath>
using namespace std;

int main(void){
	double q;

	while(cin>>q && q!=-1){
		double x = q / 2;

		while( fabs(pow(x,3) - q) >= 0.00001 * q ){
			x = x - (pow(x,3) - q) / (3 * pow(x,2));
		}

		printf("%.6lf\n",x);
	}

	return 0;
}