import java.util.*; import java.io.*; import java.math.*;
public class Main{
	//Don't have to see. start------------------------------------------
	static class InputIterator{
		ArrayList<String> inputLine = new ArrayList<String>(1024);
		int index = 0; int max; String read;
		InputIterator(){
			BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
			try{
				while((read = br.readLine()) != null){
					inputLine.add(read);
				}
			}catch(IOException e){}
			max = inputLine.size();
		}
		boolean hasNext(){return (index < max);}
		String next(){
			if(hasNext()){
				return inputLine.get(index++);
			}else{
				throw new IndexOutOfBoundsException("There is no more input");
			}
		}
	}
	static HashMap<Integer, String> CONVSTR = new HashMap<Integer, String>();
	static InputIterator ii = new InputIterator();//This class cannot be used in reactive problem.
	static PrintWriter out = new PrintWriter(System.out);
	static void flush(){out.flush();}
	static void myout(Object t){out.println(t);}
	static void myerr(Object t){System.err.print("debug:");System.err.println(t);}
	static String next(){return ii.next();}
	static boolean hasNext(){return ii.hasNext();}
	static int nextInt(){return Integer.parseInt(next());}
	static long nextLong(){return Long.parseLong(next());}
	static double nextDouble(){return Double.parseDouble(next());}
	static ArrayList<String> nextStrArray(){return myconv(next(), 8);}
	static ArrayList<String> nextCharArray(){return myconv(next(), 0);}
	static ArrayList<Integer> nextIntArray(){
		ArrayList<String> input = nextStrArray(); ArrayList<Integer> ret = new ArrayList<Integer>(input.size());
		for(int i = 0; i < input.size(); i++){
			ret.add(Integer.parseInt(input.get(i)));
		}
		return ret;
	}
	static ArrayList<Long> nextLongArray(){
		ArrayList<String> input = nextStrArray(); ArrayList<Long> ret = new ArrayList<Long>(input.size());
		for(int i = 0; i < input.size(); i++){
			ret.add(Long.parseLong(input.get(i)));
		}
		return ret;
	}
	static String myconv(Object list, int no){//only join
		String joinString = CONVSTR.get(no);
		if(list instanceof String[]){
			return String.join(joinString, (String[])list);
		}else if(list instanceof ArrayList){
			return String.join(joinString, (ArrayList)list);
		}else{
			throw new ClassCastException("Don't join");
		}
	}
	static ArrayList<String> myconv(String str, int no){//only split
		String splitString = CONVSTR.get(no);
		return new ArrayList<String>(Arrays.asList(str.split(splitString)));
	}
	public static void main(String[] args){
		CONVSTR.put(8, " "); CONVSTR.put(9, "\n"); CONVSTR.put(0, "");
		solve();flush();
	}
	//Don't have to see. end------------------------------------------
	static void solve(){//Here is the main function
    ArrayList<Integer> one = nextIntArray();
	int N = one.get(0);
	int K = one.get(1);
	ArrayList<String> list = nextCharArray();
    list.add("");
	ArrayList<Integer> plist = new ArrayList<Integer>();
	ArrayList<Integer> nlist = new ArrayList<Integer>();
    plist.add(0);
    nlist.add(0);
	for(int i = 0; i < N; i++){
		if(list.get(i).equals("1")){
            plist.set(plist.size() - 1, plist.get(plist.size() - 1) + 1);
            if(i == N - 1){
              continue;
            }
			if(list.get(i + 1).equals("0")){
				plist.add(0);
			}
		}else{
			nlist.set(nlist.size() - 1, nlist.get(nlist.size() - 1) + 1);
            if(i == N - 1){
              continue;
            }
			if(list.get(i + 1).equals("1")){
				nlist.add(0);
			}
		}
	}
	if(nlist.get(nlist.size() - 1) == 0){
		nlist.remove(nlist.size() - 1);
	}
	if(nlist.size() == plist.size()){
		plist.add(0, 0);
	}
	if(nlist.size() <= K){
		myout(N);
		return;
	}
      
	int max = plist.get(0);
	int sum = plist.get(0);
	for(int i = 0; i < nlist.size(); i++){
		sum += plist.get(i + 1) + nlist.get(i);
		if(i >= K){
			sum -= plist.get(i - K) + nlist.get(i - K);
		}
		max = Math.max(max, sum);
	}
	myout(max);
	}
	//Method addition frame start



	//Method addition frame end
}


Measured memory_bytes: 45436