main :: IO ()
main = do
    n <- readLn :: IO Int
    as1 <- sum' <$> getInts
    as2 <- reverse . sum' . reverse <$> getInts
--    print as1
--    print as2
    print $ solve n as1 as2

getInts :: IO [Int]
getInts = map read . words <$> getLine

solve n as1 as2 = maximum $
                  flip map [0..n - 1] $ \i ->
                                         as1 !! i + as2 !! i

sum' = scanl1 (+)
