Scanf.scanf "%d" (fun n ->
    let module M = Map.Make (struct type t = int let compare = compare end) in

    let rec loop i map =
        if i = n then map else
            let map = Scanf.scanf " %d"(fun a ->
                M.add a (1 + try M.find a map with _ -> 0) map)
            in
            loop (i + 1) map
    in
    let map = loop 0 M.empty in
    M.fold (fun k v acc -> if v = 1 then acc + 1 else acc) map 0 |> Printf.printf "%d\n"
)