let n = Scanf.scanf " %d" @@ (+) 0
let ps = Array.init n @@ fun _ -> Scanf.scanf " %d" @@ (+) 0
let ans = ref 0
let _ =
  for i = 0 to n - 3 do
    if (ps.(i) < ps.(i + 1) && ps.(i + 1) < ps.(i + 2)) || (ps.(i + 2) < ps.(i + 1) && ps.(i + 1) < ps.(i)) then incr ans done;
  Printf.printf "%d\n" !ans