import Data.List
import Data.Ord
import Control.Monad

main = do
 [n,_] <- map read . words <$> getLine
 ds <- map read . words <$> getContents
 print (clean n ds)

clean n = sum . take n . unfoldr move . sortBy (comparing abs)
 where move ds = guard ((not.null) ds) >> return (abs (head ds), map (subtract (head ds)) (tail ds))