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

int main() {
    while (true) {
        int q;
        cin >> q;
        if (q == -1) {
            break;
        }
        double x = q / 2.0;
        while (fabs(pow(x, 3) - q) >= q * 0.00001) {
            x -= (pow(x, 3) - q) / 3 / pow(x, 2);
        }
        printf("%f\n", x);
    }
}