import Control.Applicative
import Data.Char (digitToInt)

main :: IO ()
main = solve <$> f <*> getLine >>= print
  where
    f = map read <$> words <$> getLine

solve :: [Int] -> String -> Int
solve [_, k] s = f 0 0 0 . cycle $ map digitToInt s
  where
    f bc ic at xs
      | ic >= k = bc
      | at > 0 = let ls = take at xs
                 in f bc (ic+at) (sum ls) (drop at xs)
      | otherwise = f (bc+1) (ic+1) (head xs) (tail xs)