minimumOrders :: [Integer] -> Integer
minimumOrders (x : y : l : _)
    | y >= 0 && x == 0 = ceil y l
    | y >= 0 && x /= 0 = 1 + (ceil y l) + (flip ceil l $ abs x)
    | otherwise        = 2 + (flip ceil l $ abs x) + (flip ceil l $ abs y)
    where ceil n m = flip div m $ n + m - 1

main :: IO ()
main = print . minimumOrders . map read . lines =<< getContents