Scanf.scanf "%d" (fun n ->
    let a = Array.init n (fun _ -> Scanf.scanf " %d" (fun a -> a)) in
    let rec loop_i i acc =
        if i = n - 2 then acc else
            let b = a.(i) in
            let c = a.(i + 1) in
            let d = a.(i + 2) in
            let s = b + c + d in
            let m = s - max b (max c d) - min b (min c d) in
            let acc = if b <> c && c <> d && d <> b && (m = b || m = d) then acc + 1 else acc in
            loop_i (i + 1) acc
    in
    loop_i 0 0 |> Printf.printf "%d\n"
)