Scanf.scanf "%s" (fun s ->
    let n = String.length s in
    let rec loop i cur =
        if i = n then cur else
            if s.[i] = 'L' then loop (i + 1) (cur * 2)
                           else loop (i + 1) (cur * 2 + 1)
    in
    loop 0 1 |> Printf.printf "%d\n"
)