#include <bits/stdc++.h>
using namespace std;

int main(){
    double q;
    while(cin >> q, q!=-1){
        double x = 2/q;
        while(abs(pow(x, 3)-q)>=0.00001){
            x = x - (pow(x, 3)-q)/(3*pow(x, 2));
        }
        printf("%lf\n", x);
    }
}