#include <bits/stdc++.h>

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