import Data.Maybe
import Data.IORef
import qualified Data.ByteString.Char8 as B
import qualified Data.Vector as V
import Control.Applicative

main :: IO ()
main = do
  rd <- intReader
  [n, k] <- rd 2
  cv <- V.fromList <$> rd n
  print (solve cv k)

solve :: V.Vector Int -> Int -> Int
solve cv k = minimum [f i | i <- [0..min k (n-1)]]
  where
  n = V.length cv
  f i = let x = g (i + 2 * k + 1) in if x == maxBound then x else cv V.! i + x
  g i 
    | j < n && i >= n = maxBound
    | i >= n = 0
    | otherwise = f i
    where
    j = i - k

intReader :: IO (Int -> IO [Int])
intReader = do
  ws <- fmap ((concatMap B.words) . B.lines) B.getContents >>= newIORef
  return $ \n -> do
    xs <- readIORef ws
    writeIORef ws (drop n xs)
    return (take n . map (fst . fromJust . B.readInt) $ xs)