import Control.Applicative
import Data.List
import Data.Char (digitToInt)

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

solve :: [Int] -> String -> Int
solve [n, k] s
  | q == 0 = fst . ice 0 $ take r is
  | cb <= cat = cb
  | otherwise = cb + (q-1) * (cb - cat) + (fst . ice cat $ take r is)
  where
    is = map digitToInt s
    (q, r) = divMod k n
    (cb, cat) = ice 0 is

ice :: Int -> [Int] -> (Int, Int)
ice at ibs = f 0 at ibs
  where
    f cib cat [] = (cib, cat)
    f cib cat xs
      | cat == 0 = f (cib + 1) (head xs) (tail xs)
      | otherwise = let (as, bs) = splitAt cat xs
                    in f cib (cat - length as + sum as) bs