#include <iostream>
#include <cmath>

int main(){
    int q;
    double x;
    while(1){
        std::cin >> q;
        if(q == -1){
            return 0;
        }
        x = q / 2.0;
        while(std::abs(x * x * x - q) >= 0.00001d * q){
            x = x - (x * x * x - q) / 3 / x / x;
        }
        std::cout << x << std::endl;
    }
}