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

solve :: Integral a => [a] -> a
solve []  = 0
solve [v] = v
solve vs  = max t1 t2
    where
        t1 = head vs + solve (drop 2 vs)
        t2 = solve (tail vs)