// 2011/05/24 Tazoe

#include <iostream>
using namespace std;

int main()
{
	while(true){
		int q;
		cin >> q;
		if(q==-1)
			break;

		double x = (double)q/2.0;
		while(true){
			double err = x*x*x-(double)q;
			if(err<0.0)
				err *= -1.0;
			if(err<0.00001*(double)q)
				break;

			x = x-err/(3.0*x*x);
		}

		cout.precision(6);
		cout << fixed << x << endl;
	}

	return 0;
}