#include <iostream>
#include <string>
#include <vector>
#include <cmath>
using namespace std;

int main() {
    int q;
    while (cin >> q, q != -1) {
        double x = q / 2.0;
        double eps = 0.0001 * q;
        while (eps <= abs(x*x*x - q)) {
            x = x - (x*x*x - q) / (3*x*x);
        }
        cout.precision(6);
        cout << fixed << x << endl;
    }
    return 0;
}