#include<iostream>
#include<iomanip>
#include<cmath>

const double EPS = 1e-5;

double q;

int main()
{
	while( std::cin >> q, q != -1 )
	{
		double prv = q / 2.0, crt;

		do
		{
			crt = prv - ( pow( prv, 3.0 ) - q ) / ( 3 * pow( prv, 2.0 ) );
			prv = crt;
		}while( abs( pow( crt, 3.0 ) - q ) >= EPS * q );

		std::cout << std::setprecision( 7 ) << crt << std::endl;
	}

	return 0;
}