#include <iostream>
#include <iomanip>
#include <cmath>

int main(){
    int q;
    double x;
    std::cout << std::setprecision(6) << std::fixed;
    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 * 2 / 3 + q / x / x / 3;
        }
        std::cout << x << std::endl;
    }
}