#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;
}

vector<int> compress(int n, int k, string& s) {
	vector<int> ret;
	int prev = 1;
	int prev_index = 0;
	int i;
	for(i = 0; i < n; i++) {
		if(s[i] - '0' != prev) {
			ret.push_back(i - prev_index);
			prev = s[i] - '0';
			prev_index = i;
		}
	}
	ret.push_back(i - prev_index);
	if(prev == 0) {
		ret.push_back(0);
	}
	return ret;
}

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

	auto compressed = compress(n, k, s);
	int m = compressed.size();
	ll shakutori = 0;
	REP(i, min(k * 2 + 1, m)) { shakutori += compressed[i]; }
	ll result = shakutori;
	for(int i = 2; i + k * 2 < m; i += 2) {
		shakutori -= compressed[i - 2];
		shakutori -= compressed[i - 1];
		shakutori += compressed[i + k * 2 - 1];
		shakutori += compressed[i + k * 2];
		chmax(result, shakutori);
	}

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


Measured memory_bytes: 4092