readlines.map(&:to_f).each{|q|
  break if q == -1
  x = q / 2.0
  x2 = x*x
  x3 = x*x2
  loop do
    break if (x3 - q).abs < 0.00001 * q
    x -=  (x3 - q)/(3.0*x2)
    x2 = x*x
    x3 = x*x2
  end
  puts "%.8f" % x
}