main :: IO ()
main = do
    _n <- getLine
    getLine >>= print . solve . map read . words

solve :: [Int] -> Int
solve v = solve' v ((0, 0), (0, 0), (0, 0))
    where solve' :: [Int] -> ((Int, Int), (Int, Int), (Int, Int)) -> Int
          solve' [] (_, _, (e, f)) = max e f
          solve' (h:t) ((a, b), (c, d), e) =
              solve' t ((c, d), e, (h + max c d, h + max a b))