#include <iostream>
#include <algorithm>
#include <cmath>
#include <cstdio>
using namespace std;

int main() {
    while (true) {
        int q;
        cin >> q;
        if (q == -1) return 0;
        double x = q / 2.0;
        for ( ; ; ) {
            double res = x * x * x - q;
            if (fabs(res) < 0.00001 * q) break;
            double xnext = x - res / (3 * x * x);
            x = xnext;
        }
        printf("%.6lf\n", x);
    }
}