
open Scanf
open Printf

let flip f x y = f y x

let rec range a b = if a >= b then [] else a :: range (a+1) b

let read_int () = scanf " %d" (fun x -> x)
let rec read_ints n = if n = 0 then [] else let i = read_int () in i :: read_ints (n-1)

let rec for_iter a b f = if a >= b then [] else let x = f a in x :: for_iter (a+1) b f
let rec for_iter_ a b f = if a >= b then () else (f a; for_iter_ (a+1) b f)

let () =
  let count = Array.make 100010 0 in
  read_int ()
  |> read_ints
  |> List.iter (fun x ->
      count.(x) <- count.(x) + 1;
      count.(x+1) <- count.(x+1) + 1;
      if x > 0 then count.(x-1) <- count.(x-1) + 1);
  Array.fold_left max 0 count
  |> printf "%d\n"

