module Cp : sig
  val string_1_list_of_string: string -> string list
  val split_on_char: char -> string -> string list
  val read_int_list: unit -> int list
end =
struct
  let string_1_list_of_string x =
    String.to_seq x
    |> List.of_seq
    |> List.map (String.make 1);;

  let split_on_char sep s =
    (* from OCaml Standard Library 4.12 *)
    let r = ref [] in
    let j = ref (String.length s) in
    for i = String.length s - 1 downto 0 do
      if String.unsafe_get s i = sep then begin
        r := String.sub s (i + 1) (!j - i - 1) :: !r;
        j := i
      end
    done;
    String.sub s 0 !j :: !r;;

  let read_int_list () =
    read_line () |> split_on_char ' ' |> List.map int_of_string;;
end

let memo_rec f =
  let h = Hashtbl.create 10000 in
  let rec g x =
    let try_find = Hashtbl.find_opt h x in
    match try_find with
    | Some (x) -> x
    | None ->
      let y = f g x in
      Hashtbl.add h x y ;
      y
  in
  g;;

let sushi_memo sushi_array =
  let rec fib self =
    fun x ->
      if x < 1 then 0
      else max ((self (x - 2)) + sushi_array.(x - 1)) (self (x - 1))
  in
  memo_rec fib;;

let () =
  let n = read_int () in
  let sushi_array = Cp.read_int_list () |> Array.of_list in
  let lets_sushi_party = sushi_memo sushi_array in
  lets_sushi_party n |> print_int;
  print_newline ();;