#include <iostream>
#include <iomanip>
#include <math.h>
using namespace std;
int main( void )
{
	int qi;
	while ( cin >> qi && qi != -1 )
	{
		long double q = (long double)qi;
		long double x = q/2.0;
		while ( fabs( x*x*x - q ) >= 0.00001 * q )
		{
			long double next_x = x - (x*x*x-q) / (3 * x * x);
			x = next_x;
		}
		cout.setf( ios::fixed, ios::floatfield );
		cout << setprecision( 6 );
		cout << x << endl;
	}
}