{-# LANGUAGE BangPatterns #-}
{-# LANGUAGE BinaryLiterals #-}
{-# LANGUAGE MultiWayIf #-}
{-# LANGUAGE NumDecimals #-}
{-# LANGUAGE ScopedTypeVariables #-}
{-# LANGUAGE TupleSections #-}

import Control.Applicative
import Control.Arrow
import Control.Monad
import Control.Monad.ST

import Data.Char
import Data.List
import Data.Maybe

import qualified Data.ByteString.Char8 as B

import Data.Array.ST.Safe
import Data.STRef

import Debug.Trace
import Text.Printf

readInt = readLn :: IO Int
readInts = map ( fst . fromJust . B.readInt ) . B.words <$> B.getLine
readNInts = readInt >>= flip replicateM readInt

which a b f = if f then a else b
mp [ a, b ] = ( a, b )

main = do
	[ n, k ] <- readInts
	s <- getLine
	let
		ps = map ( head &&& length ) $ group s
		k' = min k $ length $ filter ( ( == '0' ) . fst ) ps
		r = sum $ map snd $ take ( k' * 2 ) ps
	print $ maximum $ solve r ps $ drop ( k' * 2 ) ps

solve res _ [] = [ res ]
solve res ( p : ps ) ( q : qs )
	| fst p == '1' = res + snd q : solve res' ps qs
	| otherwise = res : solve res' ps qs
	where
		res' = res - snd p + snd q