#include <iostream>
using namespace std;

/** Problem0080 : Third Root **/
int main()
{
	double x, oldX, in;
	
	while (cin >> in) {
		if (in == -1) break;
		
		oldX = in/2.0;
		for (;;) {
			x = oldX - (oldX*oldX*oldX-in)/(3*oldX*oldX);
			
			if (x*x*x > in) {
				if (x*x*x - in < 0.00001*in)
					break;
				else
					oldX = x;
			} else {
				if (in - x*x*x < 0.00001*in)
					break;
				else
					oldX = x;
			}
		}
		printf("%.6lf\n", x);
	}
	
	return 0;
}