let rec get_nth (xs: string list)(n: int) : string =
  if n < 1 then
    failwith "n must be a positive integer >= 1"

  if n > List.length xs then
    failwith "n must be less than or equal to the length of the list"

  match xs with
  | [] -> failwith "the list cannot be empty"
  | z::zs ->
    if n = 1 then
      z
    else
      get_nth zs (n - 1)