#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using ull = unsigned long long;

#define REP(i,n) for(long long i = 0; i < (n); i++)
#define FOR(i, m, n) for(long long i = (m);i < (n); ++i)
#define ALL(obj) (obj).begin(),(obj).end()
#define SPEED cin.tie(0);ios::sync_with_stdio(false);


template<class T> using V = vector<T>;
template<class T, class U> using P = pair<T, U>;

const ll MOD = (ll)1e9 + 7;
const ll MOD2 = 998244353;
const ll HIGHINF = (ll)1e18;
const ll LOWINF = (ll)1e15;
const long double PI = 3.1415926535897932384626433;

template <class T> void corner(bool flg, T hoge) {if (flg) {cout << hoge << endl; exit(0);}}
template <class T, class U>ostream &operator<<(ostream &o, const map<T, U>&obj) {o << "{"; for (auto &x : obj) o << " {" << x.first << " : " << x.second << "}" << ","; o << " }"; return o;}
template <class T>ostream &operator<<(ostream &o, const set<T>&obj) {o << "{"; for (auto itr = obj.begin(); itr != obj.end(); ++itr) o << (itr != obj.begin() ? ", " : "") << *itr; o << "}"; return o;}
template <class T>ostream &operator<<(ostream &o, const multiset<T>&obj) {o << "{"; for (auto itr = obj.begin(); itr != obj.end(); ++itr) o << (itr != obj.begin() ? ", " : "") << *itr; o << "}"; return o;}
template <class T>ostream &operator<<(ostream &o, const vector<T>&obj) {o << "{"; for (int i = 0; i < (int)obj.size(); ++i)o << (i > 0 ? ", " : "") << obj[i]; o << "}"; return o;}
template <class T, class U>ostream &operator<<(ostream &o, const pair<T, U>&obj) {o << "{" << obj.first << ", " << obj.second << "}"; return o;}
template <template <class tmp>  class T, class U> ostream &operator<<(ostream &o, const T<U> &obj) {o << "{"; for (auto itr = obj.begin(); itr != obj.end(); ++itr)o << (itr != obj.begin() ? ", " : "") << *itr; o << "}"; return o;}
void print(void) {cout << endl;}
template <class Head> void print(Head&& head) {cout << head;print();}
template <class Head, class... Tail> void print(Head&& head, Tail&&... tail) {cout << head << " ";print(forward<Tail>(tail)...);}
template <class T> void chmax(T& a, const T b){a=max<T>(a,b);}
template <class T> void chmin(T& a, const T b){a=min<T>(a,b);}
void YN(bool flg) {cout << ((flg) ? "YES" : "NO") << endl;}
void Yn(bool flg) {cout << ((flg) ? "Yes" : "No") << endl;}
void yn(bool flg) {cout << ((flg) ? "yes" : "no") << endl;}

int main() {
	int N,K; cin >> N >> K;
	string S; cin >> S;
	S = "." + S + ".";
	V<P<int,int>> a;
	for(int i = 0; i < N+2; ++i){
		
		if(S[i]=='1'){
			int l = i;
			int r = i;
			for(;r < N+2; ++r){
				if(S[r] != '1') break;
			}
			r--;
			i = r;
			a.push_back({l,r});
		}
	}
	int M = a.size();
	corner(M==0,N);
	int ans = 0;
	if(a[0].first!=1){
		int cnt = 0;
		for(int i = 0; i < K && i < M; ++i){
			cnt = a[i].second;
		}
		chmax(ans,cnt);
	}
	if(a[M-1].second!=N){
		int cnt = 0;
		for(int i = 0; i < K && 0 <= M-1 - i; ++i){
			cnt = N - a[M-1 - i].first + 1;
		}
		chmax(ans,cnt);
	}
	if(a[0].first!=1 && a[M-1].second!=N && a.size()+1<=K) chmax(ans,N);
	for(int i = 0; i + K < M; ++i){
		chmax(ans,a[i+K].second - a[i].first + 1);
	}
	if(M-1<=K) chmax(ans,a[M-1].second-a[0].first + 1);

	cout << ans << endl;
	
	
	return 0;
}


Measured memory_bytes: 1016