{-# OPTIONS_GHC -O2 #-}
{-# LANGUAGE BangPatterns, CPP, FlexibleContexts, FlexibleInstances         #-}
{-# LANGUAGE KindSignatures, LambdaCase, MagicHash, MultiParamTypeClasses   #-}
{-# LANGUAGE MultiWayIf, OverloadedStrings, RecordWildCards                 #-}
{-# LANGUAGE ScopedTypeVariables, TupleSections, TypeFamilies, ViewPatterns #-}

import           Control.Applicative
import           Control.Exception
import           Control.Monad
import           Control.Monad.Primitive
import           Control.Monad.ST
import           Control.Monad.State.Strict
import           Data.Bool
import qualified Data.ByteString             as B
import qualified Data.ByteString.Builder     as B
import qualified Data.ByteString.Char8       as C
import qualified Data.ByteString.Internal    as B
import qualified Data.ByteString.Unsafe      as B
import           Data.Char
import qualified Data.Foldable               as F
import           Data.Function
import           Data.Functor.Identity
import qualified Data.IntMap.Strict          as IM
import qualified Data.IntSet                 as IS
import qualified Data.List                   as L
import qualified Data.Map.Strict             as M
import           Data.Monoid
import           Data.Ord
import           Data.Primitive.MutVar
import           Data.Ratio
import qualified Data.Set                    as S
import           Data.Tuple
import qualified Data.Vector                 as V
import qualified Data.Vector.Generic         as G
import qualified Data.Vector.Generic.Mutable as GM
import qualified Data.Vector.Mutable         as VM
import qualified Data.Vector.Unboxed         as U
import qualified Data.Vector.Unboxed.Mutable as UM
import           Debug.Trace
import           Foreign                     hiding (void)
import           GHC.Exts
import qualified System.IO                   as IO
import           Unsafe.Coerce

main :: IO ()
main = do
    n <- readLn :: IO Int
    xs <- U.unfoldrN n (runParser int) <$> C.getLine
    print $ solve n xs

solve :: Int -> U.Vector Int ->Int
solve n xs = U.maximum $ U.generate n $ \i ->
    U.unsafeIndex os i + U.unsafeIndex es n - U.unsafeIndex es i
  where
    !m = div n 2
    !evens = U.generate n (\i -> U.unsafeIndex xs (2 * i))
    !odds = U.generate n (\i -> U.unsafeIndex xs (2 * i + 1))
    !es = U.scanl (+) 0 evens
    !os = U.scanl (+) 0 odds


-------------------------------------------------------------------------------
-- Utils
-------------------------------------------------------------------------------
rep :: Monad m => Int -> (Int -> m ()) -> m ()
rep !n = U.forM_ $ U.generate n id
{-# INLINE rep #-}
rev :: Monad m => Int -> (Int -> m ()) -> m ()
rev !n = U.forM_ $ U.iterateN n (subtract 1) (n - 1)
{-# INLINE rev #-}
infixl 8 `shiftRL`, `unsafeShiftRL`
shiftRL = unsafeShiftRL
{-# INLINE shiftRL #-}
unsafeShiftRL (I# x#) (I# i#) = I# (uncheckedIShiftRL# x# i#)
{-# INLINE unsafeShiftRL #-}
type Parser a = StateT C.ByteString Maybe a
runParser :: Parser a -> C.ByteString -> Maybe (a, C.ByteString)
runParser = runStateT
{-# INLINE runParser #-}
int :: Parser Int
int = coerce $ C.readInt . C.dropWhile isSpace
{-# INLINE int #-}
int1 :: Parser Int
int1 = fmap (subtract 1) int
{-# INLINE int1 #-}
char :: Parser Char
char = coerce C.uncons
{-# INLINE char #-}
byte :: Parser Word8
byte = coerce B.uncons
{-# INLINE byte #-}
-------------------------------------------------------------------------------
-- Data.FenwickTree
-------------------------------------------------------------------------------
newtype FenwickTree s a = FenwickTree{getFenwickTree :: UM.MVector s a}
newFenwickTree :: (PrimMonad m, U.Unbox a, Num a) => Int -> m (FenwickTree (PrimState m) a)
newFenwickTree n = FenwickTree <$> UM.replicate (n + 1) 0
buildFenwickTree :: (PrimMonad m, U.Unbox a, Num a) => U.Vector a -> m (FenwickTree (PrimState m) a)
buildFenwickTree vec = do { let { n = U.length vec}; ft <- UM.replicate (n + 1) 0; U.unsafeCopy (UM.tail ft) vec; U.forM_ (U.generate n (+ 1)) $ \ i -> do { let { j = i + (i .&. (-i))}; when (j <= n) $ do { fti <- UM.unsafeRead ft i; UM.unsafeModify ft (+ fti) j}}; return $ FenwickTree ft}
getFreezeFenwickTree :: (PrimMonad m, U.Unbox a) => FenwickTree (PrimState m) a -> m (U.Vector a)
getFreezeFenwickTree (FenwickTree ft) = do { U.freeze ft}
sumTo :: (PrimMonad m, U.Unbox a, Num a) => Int -> FenwickTree (PrimState m) a -> m a
sumTo k (FenwickTree ft) = go 0 k where { go !acc !i | i > 0 = do { xi <- UM.unsafeRead ft i; go (acc + xi) (i - (i .&. (-i)))} | otherwise = return acc}
{-# INLINE sumTo #-}
sumFromTo :: (PrimMonad m, U.Unbox a, Num a) => Int -> Int -> FenwickTree (PrimState m) a -> m a
sumFromTo l r ft = (-) <$> sumTo r ft <*> sumTo l ft
{-# INLINE sumFromTo #-}
addAt :: (PrimMonad m, U.Unbox a, Num a) => Int -> a -> FenwickTree (PrimState m) a -> m ()
addAt k v (FenwickTree ft) = flip fix (k + 1) $ \ loop !i -> do { when (i < n) $ do { UM.unsafeModify ft (+ v) i; loop $ i + (i .&. (-i))}} where { n = UM.length ft}
{-# INLINE addAt #-}
findMaxIndexLT :: (PrimMonad m, U.Unbox a, Num a, Ord a) => a -> FenwickTree (PrimState m) a -> m Int
findMaxIndexLT w0 (FenwickTree ft) | w0 <= 0 = return 0 | otherwise = go w0 highestOneBit 0 where { n = UM.length ft; highestOneBit = until (> n) (* 2) 1 `quot` 2; go !w !step !i | step == 0 = return i | otherwise = do { if i + step < n then do { u <- UM.unsafeRead ft (i + step); if u < w then go (w - u) (step `unsafeShiftR` 1) (i + step) else go w (step `unsafeShiftR` 1) i} else go w (step `unsafeShiftR` 1) i}}
{-# INLINE findMaxIndexLT #-}
