main = do
  x <- fmap read getLine :: IO Int
  y <- fmap read getLine :: IO Int
  l <- fmap read getLine :: IO Int
  let
    u = if y >= 0 then div (y-1) l + 1 else 0
    s = if x == 0 then 0 else 1 + div (abs x - 1) l + 1
    d = if y < 0 then 1 + div ((-y)-1) l + 1 else 0
  putStrLn $ show $ u+s+d