let ``No.104 国道``() =
  let rec loop acc lt =
    match lt with
    | []    -> acc
    | x::xs -> match x with
               | 'L' -> loop (acc * 2) xs
               | 'R' -> loop (acc * 2 + 1) xs
               | _   -> acc
               
  stdin.ReadLine()
  |> Seq.toList
  |> loop 1
  |> stdout.WriteLine

``No.104 国道``()