-module(solution).
-export([main/0]).

-compile(export_all).

main() ->
    { ok, [N]} = io:fread("", "~d"),
    A = lists:sort(read_array(N,"~d")),
    io:format("~p~n", [solve(A)]),
    true.

read_array(0,_) -> [];
read_array(N,D) -> 
   {ok, [X]} = io:fread("", D),
   [X | read_array(N-1,D)].

solve (List) ->
  Orddict =
    lists:foldl(
	  fun (N, D) -> orddict:update_counter(N, 1, D) end,
	  orddict:new(),
	  List),
  fun
    Split ([], MaxCount) -> MaxCount;
    Split ([{A,CA}, {B,CB} | T], MaxCount) when B == A+1 andalso CA+CB > MaxCount ->
      Split([{B,CB} | T], CA+CB);
    Split ([{_,CA} | T], MaxCount) when CA > MaxCount ->
      Split(T, CA);
    Split ([{_,CA}], MaxCount) when CA > MaxCount ->
      CA;
    Split ([_ | T], MaxCount) -> Split(T, MaxCount)
  end (Orddict, 0).
      
 %% |