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

let rec solve acc count ls =
  match ls with
  | [] -> count::acc
  | n1::[] -> (count + n1)::acc
  | n1::n2::ns ->
     let acc' = solve acc (n1 + count) ns in
     solve acc' (n2 + count) (if List.length ns > 0 then List.tl ns else [])

let _ =
  let _ = int_of_string @@ read_line() in
  let inputs = String.split_on_char ' ' (read_line ()) in
  solve [] 0 (List.map (fun i -> int_of_string i) inputs)
  |> List.fold_left (fun acc v -> max acc v) (-1)
  |> print_int