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

int main(){
    double x, q;
    while(cin >> q, q != -1.0){
        x = q / 2.0;
        while(abs(x*x*x-q) >= 0.00001*q){
            x = x-(x*x*x-q)/(3*x*x);
        }
        printf("%.6f\n", x);
    }
    return 0;
}