#ifdef LOCAL
#include <cstdio>
#include <vector>
#include <algorithm>
#include <iostream>
#include <cstring>
#else
#include <bits/stdc++.h>
#endif
using namespace std ;

typedef long long ll ;
typedef unsigned long long ull ;
#define rep(i , n ) for ( int i =0; i < n ; i++)
#define rrep(i , n) for ( int i = n-1; i >=0 ; i--)

#define _sort(arg) sort(begin(arg), end(arg))
#define MOD 1000000007
#define pb push_back
#define DEBUG(x) cout << #x << ": " << x << endl;

class UnionFind {
private:
	ull size_; 
	std::vector<ull> par, rank, count;

public:
	UnionFind() : size_(0), par(std::vector<ull>()), rank(std::vector<ull>()), count(std::vector<ull>()) {};
	UnionFind(ull size__) : size_(size__) {
		par.resize(size_); rank.resize(size_); count.resize(size__);
		for (ull i = 0; i < size_; i++) par[i] = i, rank[i] = 0, count[i] = 1;
	}
	ull size() { return size_; }
	// ull root(ull x) { return par[x] == x ? x : par[x] = root(par[x]); }
	
	ull root(ull x)
	{
		while(par[x] != x)
		{
			par[x] = par[par[x]];
			x = par[x];
		}
		return x;
	}
	
	bool same(ull x, ull y) { return root(x) == root(y); }

	void unite(ull x, ull y) {
		x = root(x), y = root(y);
		if (x == y) return;
		if (rank[x] < rank[y]) par[x] = y, count[y]+=count[x], count[x]=0;
		else if (rank[x] == rank[y]) par[y] = x, rank[x]++, count[x]+=count[y], count[y]=0;
		else par[y] = x, count[x] += count[y], count[y] = 0;
	}

	ull size__(ull x)
	{
		return count[root(x)];
	}

	bool operator==(const UnionFind &u) { return par == u.par; }
	bool operator!=(const UnionFind &u) { return par != u.par; }
};
/*
maybe sth wrong 
got wa in one problem
*/
ll modpow(ll a, ll b)
{
	if (b == 0)
	{
		return 1;
	}

	if (b % 2)
	{
		return a * modpow(a, b-1) % MOD;
	}
	else
	{
		ll halfB = b / 2;
		ll half = modpow(a, halfB);
		return half * half % MOD;
	}
}

ll calcComb(ll n, ll m)
{
	if (m > n-m)
	{
		return calcComb(n, n-m);
	}

	ll ansMul = 1;
	ll ansDiv = 1;

	rep(i, m)
	{
		ansMul *= (n-i);
		ansDiv *= (i+1);
		ansMul %= MOD;
		ansDiv %= MOD;
	}

	return ansMul * modpow(ansDiv, MOD - 2) % MOD;
}

__attribute__((constructor))
void initial()
{
	cin.tie(NULL);
	ios::sync_with_stdio(false);
}


int main()
{
	int N, K;
	
	cin >> N >> K;
	
	string s;
	cin >> s;

	//cout << "size = " << s.size() << endl;

	int cur = 0;
	vector<int> v;
	int now = 1;
	int cnt = 0;
	rep(i, s.size())
	{
		if (s[i] == (char)('0' + now))
		{
			cnt++;
		}
		else
		{
			v.pb(cnt);
			cnt = 1;
			now = 1-now; // now ^= 1;
		}
	}
	if (cnt)
	{
		v.pb(cnt);
	}

	if (v.size() % 2 == 0)
	{
		v.pb(0);
	}

	#if 0
	// 尺取り法
	int ans = 0;
	int left = 0;
	int right = 0;
	int tmp = 0;
	int add = 2 * K + 1;
	for (int i = 0; i < v.size(); i+=2)
	{
		int nextleft = i;
		int nextright = min(i + add, (int)v.size());
		while(nextleft > left)
		{
			tmp -= v[left];
			left++;
		}

		while(nextright > right)
		{
			tmp += v[right];
			right++;
		}

		ans = max(ans, tmp);
	}

	cout << ans << endl;
	#endif

	// 累積和
	int ans = 0;
	int add = 2 * K + 1;
	vector<int> sum(v.size() + 1);
	for (int i = 0; i < v.size(); i+=1)
	{
		sum[i+1] = sum[i] + v[i];
	}

	for(int i = 0; i < v.size(); i+=2)
	{
		int left = i;
		int right = min(i+add, (int)v.size());
		int tmp = sum[right] - sum[left];
		ans = max(ans, tmp);
	}

	cout << ans << endl;

	return 0;
}


Measured memory_bytes: 1272