solve :: [Int] -> Int
solve vs =
  aux 0
  where
    aux n
      | (drop n vs == []) = 0
      | otherwise = max ((vs !! n) + solveList !! (n + 2)) (solveList !! (n + 1))
    solveList = [aux n | n <- [0,1..]]

main :: IO ()
main = do
  n <- (read :: String -> Int) <$> getLine
  vs <- (map read . words) <$> getLine
  (putStr . show . solve) vs