let succ = function
  | [] -> assert false
  | (x, n) :: t -> (x, n+1) :: t

let rec bucks = function
  | [] -> []
  | x :: [] -> [(x, 1)]
  | x :: y :: t when x = y -> succ (bucks (y :: t))
  | x :: y :: t -> (x, 1) :: (bucks (y :: t))

let rec solve maxi = function
  | [] -> maxi
  | (_, n) :: [] -> max maxi n
  | (x, n) :: (y, m) :: t when x + 1 = y -> solve (max maxi (n + m)) ((x, m) :: t)
  | (_, n) :: (x, m) :: t -> solve (max maxi m) ((x, m) :: t)

let () =
  ignore (read_int ());
  let l = read_line () in
  let l = Str.split (Str.regexp " ") l in
  let l = List.map int_of_string l in
  let l = List.sort compare l in
  let l = bucks l in
  let n = solve 0 l in
  print_int n;
  print_newline ()