let is_kadomatsu a1 a2 a3 =
  a1 <> a3 &&
  (a1 < a2 && a3 < a2 || a1 > a2 && a3 > a2)

let solve alst =
  let rec solve' a1 a2 lst result =
    match lst with
    | [] -> result
    | x::xs ->
      let nextResult =
        if is_kadomatsu a1 a2 x then
          result + 1
        else result
      in
      solve' a2 x xs nextResult
  in
  let a1, lst = List.hd alst, List.tl alst in
  let a2, lst = List.hd lst, List.tl lst in
  solve' a1 a2 lst 0

let () =
  let _ = read_line ()
  and alst = read_line () |>
             Str.split (Str.regexp_string " ") |>
             List.map int_of_string
  in
  solve alst |> print_int;
  print_newline ()