solve :: Integer -> Integer
solve d = a * b
    where
        d'  | d < 4     = 0
            | odd d     = (d - 1) `div` 2
            | otherwise = d `div` 2
        [a, b]  | odd d'    = [(d' + 1) `div` 2, (d' - 1) `div` 2]
                | otherwise = [d' `div` 2, d' `div` 2]

main = readLn >>= print . solve