module Main where

import Data.List.Split (chunksOf)

solve :: Int -> [Int] -> Int
solve k arr =
    length -- count the True
        . filter id -- only the Trues
        . zipWith elem [1 ..] -- is the page number in the page?
        $ concatMap (chunksOf k . flip take [1 ..]) arr -- list of pages' contents

main :: IO ()
main = do
    [n, k] <- map read . words <$> getLine :: IO [Int]
    arr <- map read . words <$> getLine :: IO [Int]
    print $ solve k arr