#include<iostream>
#include<cstdio>
#include<cmath>
using namespace std;
int main() {
    while (1) {
        int q;
        cin >> q;
        if (q == -1) {
            return 0;
        }
        double n = q / 2.0;
        while (abs(pow(n, 3) - q) >= 0.00001 * q) {
            n -= (pow(n, 3) - q) / (3 * pow(n, 2));
        }
        printf("%.6f\n", n);
    }
    
}

