let () =
  Scanf.scanf "%d\n" @@ fun n ->
  let lst = Array.to_list (Array.init n @@ fun _ -> Scanf.scanf "%d " @@ fun d -> d) in
  let lst = List.fast_sort compare lst in
  let h, t = List.hd lst, List.tl lst in
  let ((cnt,ans),(buf,n)) = List.fold_left 
      (fun ((cnt,ans),(buf,n)) x -> 
        if n = x then ((cnt,ans),(buf+1,n))
        else if cnt <= buf then ((buf,n),(1,x))
        else ((cnt,ans),(1,x))) ((0,-1),(1,h)) t in
  Printf.printf "%d\n" (if cnt = buf then n else ans)