#!/usr/bin/ruby
# coding: utf-8

PI = Math.acos(-1)
EPS = 0.00001

while true
  q = gets.to_f
  break if q < 0
  x = q / 2
  while (x**3 - q).abs >= EPS * q
    x -= (x**3 - q) / 3.0 / x / x
  end
  puts x
end