main = do
    ps <- map (map read . words) . lines <$> getContents
    print $ (ps !! 1 !! 1 * ps !! 2 !! 2 + ps !! 1 !! 2 * ps !! 2 !! 1) / (ps !! 1 !! 1 + ps !! 2 !! 1)