#include <iostream>
#include <iomanip>
#include <cmath>
using namespace std;

int main(){
	int q;
	while ( cin >> q && q != -1 ){
		double x = static_cast< double >( q ) / 2;
		while ( ( ( x * x * x - q ) > 0 ? ( x * x * x - q ) : -( x * x * x - q ) ) >= 0.00001 * q ){
			x -= ( x * x * x - q ) / ( 3 * x * x );
		}

		cout << setprecision( 6 ) << setiosflags( ios::fixed );
		cout << x << endl;
	}
	return 0;
}