import           Control.Monad.State
import           Data.Char
import           Data.Coerce
import qualified Data.ByteString.Char8       as BSC8
import qualified Data.Vector.Unboxed         as VU
import qualified Data.Vector.Unboxed.Mutable as VUM

createDP :: Int -> VU.Vector Int -> VU.Vector Int
createDP n xs = VU.constructN n $ \dp -> case VU.length dp of
  0 -> xs VU.! 0
  1 -> max (xs VU.! 0) (xs VU.! 1)
  q -> max (dp VU.! (q - 1)) (xs VU.! q + (dp VU.! (q - 2)))

main :: IO ()
main = do
  n <- readLn :: IO Int
  if n == 1
    then (readLn :: IO Int) >>= print
    else do
      xs <- seqInput n
      print $ (createDP n xs) VU.! (n - 1)


type Parser a = StateT BSC8.ByteString Maybe a
runParser :: Parser a -> BSC8.ByteString -> Maybe (a, BSC8.ByteString)
runParser = runStateT
{-# INLINE runParser #-}
int :: Parser Int
int = coerce $ BSC8.readInt . BSC8.dropWhile isSpace
{-# INLINE int #-}
seqInput :: Int -> IO (VU.Vector Int)
seqInput n = VU.unfoldrN n (runParser int) <$> BSC8.getLine
{-# INLINE seqInput #-}