import Control.Monad.ST
import Control.Monad
import Data.Array.ST
import Data.Array
import Data.STRef
import Control.Monad
import Control.Applicative
import Data.List
getMin a b
  | a<0 && b<0 = negate a
  | a>0 && b>0 = b
  | otherwise = (b-a) + min (negate a) b
ans n [] c = 800000000
ans n (a:as) c
  | c < n = 800000000
  | otherwise = min (getMin a ((a:as) !! (n-1))) (ans n as (c-1))
main = do
  [n,m] <- map read <$> words <$> getLine ::IO [Int]
  b <- sort <$> map read <$> words <$> getContents ::IO [Int]
  print $ ans n b m