solve :: Integer -> Integer
solve x
    | odd x     = (n - 1) * (n + 1) + n
    | otherwise = n * (n + 1) + n
    where
        n | odd x       = div (fromIntegral(x + 1)) (fromIntegral(2 :: Integer))
          | otherwise   = div (fromIntegral(x)) (fromIntegral(2 :: Integer))

main = readLn >>= print . solve