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

using namespace std;

int main()
{
	int q;
	while (true) {
		cin >> q;
		if (q==-1) break;
		
		double q_ = static_cast<double>(q);
		double x = 0.5 * q_;
		while ( abs(x*x*x - q_) >= 0.00001 * q_ ) {
			x -= (x*x*x - q_) / (3.0*x*x);
		}
		cout << fixed << setprecision(6) << x << endl;
	}
	
	return 0;
}