defmodule Math do
  def fib(n) when n == 1, do: [0]
  def fib(n) when n > 1, do: fib([0], n-1)
  def fib([0], n), do: fib([1|[0]], n-1)
  def fib(l,0), do: Enum.reverse(l)
  def fib(l,n) do
    [h1|[h2 | _]] = l
    fib([h1+h2 | l], n-1)
  end
end