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

using namespace std;

const double eps = 0.00001;
double q;

inline double next_x(double x)
{
    return x - (x * x * x - q) / (3 * x * x);
}

int main()
{
    cout << fixed << setprecision(6);

    while (cin >> q, q != -1) {
        double xn = q / 2;

        while (abs(xn * xn * xn - q ) >= eps * q) 
            xn = next_x(xn);

        cout << xn << endl;
    }

    return 0;
}