#include <iostream>
#include <cmath>

using namespace std;

int main(int argc, char const* argv[])
{
	double answer;
	double q;

	while( cin >> q && q != -1 ){
		answer = q / 2;

		while( fabs( answer * answer * answer - q ) >= 0.00001 * q ){
			answer = answer - ( (answer * answer * answer ) - q ) / ( 3 * answer * answer );
		}

		printf("%.6f\n",answer);
	}
	return 0;
}