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

int main() {
    int q;
    while (cin >> q) {
        if (q == -1) break;
        double x = q / 2.0;
        while (true) {
            x = x - (x*x*x - q) / (3*x*x);
            if (abs(x*x*x-q) < 1e-5*q) break;
        }
        cout.precision(6);
        cout << fixed << x << endl;
    }
    return 0;
}