solve [x,y,d]
    | d == 0            = 1
    | m < d             = 0
    | x < d || y < d    = m - d + 1
    | otherwise         = d + 1
    where
        m = (abs x) + (abs y)   -- マンハッタン距離

main = do
    xyd <- map (abs . read :: String -> Int) . words <$> getLine
    print $ solve xyd