#include <iostream>
#include <cmath>

using namespace std;

void solve()
{
	int q;
	while(cin >> q, q != -1)
	{
		double eps = 0.00001 * q;
		double x = q / 2.0;
		while(fabs(x * x * x - q) > eps)
		{
			x = x - (x * x * x - q) / (3 * x * x);
		}
		printf("%.6f\n", x);
	}
}

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