#include <iostream>
#include <stdio.h>
#include <math.h>

using namespace std;

void solve()
{
	double q;
	while(cin >> q, q != -1)
	{
		double x1 = q / 2;
		while(true)
		{
			if(fabs(x1 * x1 * x1 - q) < 0.00001 * q)
			{
				printf("%.6f\n", x1);
				break;
			}
			x1 = x1 - (x1 * x1 * x1 - q) / (3 * x1 * x1);
		}
	}
}

int main()
{
	solve();
	return(0);
}