import Data.List

rInteger :: String -> Integer
rInteger = read

solve :: Int -> Int -> [Integer] -> Integer
solve 1 _ as = 0
solve n k as = foldr (+) 0 ts where
    ts = take (n - k) $ sort xs
    xs = zipWith (-) (reverse (tail as)) (reverse (init as))
main = do
    [n, k] <- map read . words <$> getLine
    as <- sort . map rInteger . words <$> getLine
    print $ solve n k as