while line = gets
  q = line.chomp.to_f
  break if q == -1

  x1 = 100
  while true
    x2 = x1 - (x1**3 - q) / (3 * x1**2)
    break if (x2 - x1).abs < 0.00001 * q
    x1 = x2
  end

  puts sprintf('%0.6f', x2)
end