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

solve :: [Int] -> Int
solve = maximum . map sum . genLists
    where genLists :: [Int] -> [[Int]]
          genLists [] = [[]]
          genLists [a] = [[a]]
          genLists [a, b] = [[a], [b]]
          genLists (a:b:c:d) = [ a:i | i <- genLists (c:d) ] ++ [ b:i | i <- genLists d ]