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

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

int main() {
    while (cin >> q, q != -1){
        double x = q/2;
        while (fabs(x*x*x - q) > 1e-5 * q) {
            x = f(x);
        }
        printf("%.10lf\n", x);
    }
}

