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

int main()
{
    int q;
    while(cin >> q, q != -1){
        double x = q / 2.0;
        while(1){
            if(abs(x * x * x - q) < 0.00001 * q){
                cout << fixed << x << endl;
                break;
            } else {
                x = x - (x * x * x - q)/(3 * x * x);
            }
        }
        //cout << fixed << cbrt((long double)q) << endl;
    }
}