let calc = function
        | [a;_;c;d;] -> max (a+c) (a+d)
        | [a;_;c;] -> a+c
        | [a;_;] | [a] -> a
        | _ -> failwith "unattainable"
    let rec f3 l n =
        match List.length l with
        | 0 -> n
        | 1 -> n+l.[0]
        | _ ->
            let A = calc <| List.truncate 4 l
            let B = calc <| (List.skip 1 >> List.truncate 3) l
            let p = if A < B then 1 else 0
            let pp =
                if List.length l < (p+3) then List.length l
                else p+2
            f3 (List.skip (pp) l) (l.[p]+n)
    stdin.ReadLine() |> ignore
    let l = stdin.ReadLine().Split([|' '|]) |> Seq.map (int) |> Seq.toList
    f3 l 0
    |> (printfn "%d")