#include <algorithm>
#include <boost/optional.hpp>
#include <climits>
#include <cmath>
#include <cstdio>
#include <cstring>
#include <functional>
#include <iomanip>
#include <iostream>
#include <limits>
#include <list>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <sstream>
#include <string>
#include <tuple>
#include <type_traits>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <vector>

#define REP(i, n) for(int i = 0, i##_MACRO = (n); i < i##_MACRO; i++)
#define RANGE(i, a, b) for(int i = (a), i##_MACRO = (b); i < i##_MACRO; i++)
#define EACH(e, a) for(auto&& e : a)
#define ALL(a) std::begin(a), std::end(a)
#define RALL(a) std::rbegin(a), std::rend(a)
#define FILL(a, n) memset((a), n, sizeof(a))
#define FILLZ(a) FILL(a, 0)
#define INT(x) (static_cast<int>(x))
#define PRECISION(x) std::fixed << std::setprecision(x)

using namespace std;

using ll = long long;
using VI = std::vector<int>;
using VI2D = std::vector<vector<int>>;
using VLL = std::vector<long long>;
using VLL2D = std::vector<vector<long long>>;

constexpr int INF = 2e9;
constexpr double EPS = 1e-10;
constexpr double PI = acos(-1.0);

constexpr int dx[] = {-1, 0, 1, 0};
constexpr int dy[] = {0, -1, 0, 1};

template <typename T, std::size_t N>
struct make_vector_type {
	using type =
		typename std::vector<typename make_vector_type<T, (N - 1)>::type>;
};

template <typename T>
struct make_vector_type<T, 0> {
	using type = typename std::vector<T>;
};

template <typename T, size_t N>
auto make_vector_impl(const std::vector<std::size_t>& ls, T init_value) {
	if constexpr(N == 0) {
		return std::vector<T>(ls[N], init_value);
	} else {
		return typename make_vector_type<T, N>::type(
			ls[N], make_vector_impl<T, (N - 1)>(ls, init_value));
	}
}

template <typename T, std::size_t N>
auto make_vector(const std::size_t (&ls)[N], T init_value) {
	std::vector<std::size_t> dimensions(N);
	for(int i = 0; i < N; i++) {
		dimensions[N - i - 1] = ls[i];
	}
	return make_vector_impl<T, N - 1>(dimensions, init_value);
}

template <typename T>
std::vector<T> make_vector(std::size_t size, T init_value) {
	return std::vector<T>(size, init_value);
}

template <typename T>
constexpr int sign(T x) {
	return x < 0 ? -1 : x > 0 ? 1 : 0;
}

template <>
constexpr int sign(double x) {
	return x < -EPS ? -1 : x > EPS ? 1 : 0;
}

template <typename T, typename U>
constexpr void chmax(T& m, U x) {
	m = max(m, x);
}

template <typename T, typename U>
constexpr void chmin(T& m, U x) {
	m = min(m, x);
}

template <typename T>
constexpr T square(T x) {
	return x * x;
}

template <typename T>
class RunLengthEncoding {
	using iterator = typename std::vector<std::pair<T, std::size_t>>::iterator;
	using const_iterator =
		typename std::vector<std::pair<T, std::size_t>>::const_iterator;

	std::vector<std::pair<T, size_t>> rle;

	public:
	template <typename U>
	RunLengthEncoding(U seq) {
		T prev = *seq.begin();
		std::size_t count = 0;
		for(T& e : seq) {
			if(e != prev) {
				this->rle.push_back(make_pair(prev, count));
				prev = e;
				count = 0;
			}
			count++;
		}
		this->rle.push_back(make_pair(prev, count));
	}

	std::vector<T> get() const { return this->rle; }

	std::size_t size() const { return this->rle.size(); }
	iterator begin() { return this->rle.begin(); }
	iterator end() { return this->rle.end(); }
	const_iterator cbegin() const { return this->rle.cbegin(); }
	const_iterator cend() const { return this->rle.cend(); }

	const std::pair<T, std::size_t>& operator[](std::size_t i) const& {
		return this->rle[i];
	}
	std::pair<T, std::size_t>& operator[](std::size_t i) & {
		return this->rle[i];
	}
	std::pair<T, std::size_t> operator[](std::size_t i) const&& {
		return std::move(this->rle[i]);
	}
};

int main() {
	int n, k;
	cin >> n >> k;
	string s;
	cin >> s;

	if(s[0] == '0') {
		s = "x"s + move(s);
	}
	if(s[n - 1] == '0') {
		s += "x"s;
	}

	auto rle = RunLengthEncoding<char>(s);
	int m = rle.size();
	if(rle[0].first == 'x') {
		rle[0].second = 0;
	}
	if(rle[m - 1].first == 'x') {
		rle[m - 1].second = 0;
	}
	ll shakutori = 0;
	REP(i, min(k * 2 + 1, m)) { shakutori += rle[i].second; }
	ll result = shakutori;
	for(int i = 2; i + k * 2 < m; i += 2) {
		shakutori -= rle[i - 2].second;
		shakutori -= rle[i - 1].second;
		shakutori += rle[i + k * 2 - 1].second;
		shakutori += rle[i + k * 2].second;
		chmax(result, shakutori);
	}

	cout << result << endl;
	return 0;
}


Measured memory_bytes: 5568