#include <iostream>
#include <iomanip>
#include <cmath>
#include <functional>
#include <algorithm>
#include <numeric>
#include <vector>
#include <list>
#include <queue>
#include <stack>
#include <deque>
#include <map>
#include <set>
#include <unordered_map>
#include <unordered_set>
#include <boost/range/irange.hpp>
#include <boost/container/static_vector.hpp>
#include <boost/utility/string_ref.hpp>
#include <boost/multiprecision/cpp_int.hpp>
#include <boost/math/common_factor_rt.hpp>

class input
{
public:
    input()
    {
        std::cin.tie(nullptr);
        std::ios::sync_with_stdio(false);
    }

    template <class T>
    inline input& operator>>(T& var) { return std::cin >> var, *this; }
    template <class T>
    inline input& operator,(T& var) { return *this >> var; }

    template <class T>
    inline T read()
    {
        T var;
        std::cin >> var;
        return var;
    }

    template <class InputIterator>
    inline void read(InputIterator head, std::size_t n)
    {
        for (std::size_t i = 0; i < n; ++i) {
            std::cin >> *head;
            ++head;
        }
    }

    template <class T>
    inline std::vector<T> read(std::size_t n)
    {
        std::vector<T> res;
        res.reserve(n);

        for (std::size_t i = 0; i < n; ++i) {
            T tmp;
            std::cin >> tmp;
            res.emplace_back(tmp);
        }
        return res;
    }

    template <class T, class F>
    inline void online(std::size_t n, F&& f)
    {
        T var;
        for (std::size_t i = 0; i < n; ++i) {
            std::cin >> var;
            f(var);
        }
    }
};
template <class T, std::size_t n>
std::istream& operator>>(std::istream& in, std::array<T, n>& var)
{
    for (std::size_t i = 0; i < n; ++i) {
        in >> var[i];
    }
    return in;
}

class output
{
    std::ostream& cout;

    template <class T, class... Args>
    void impl(T&& v, Args&&... args)
    {
        cout << std::forward<T>(v) << ' ';
        impl(std::forward<Args>(args)...);
    }
    template <class T>
    void impl(T&& v)
    {
        cout << std::forward<T>(v);
    }

public:
    output() : cout(std::cout)
    {
        cout << std::fixed << std::setprecision(15);
    }

    template <class... Args>
    void operator()(Args&&... args)
    {
        impl(std::forward<Args>(args)...);
        cout << '\n';
    }
    template <class... Args>
    void noreturn(Args&&... args)
    {
        impl(std::forward<Args>(args)...);
    }

    template <class T>
    void print(const T& container)
    {
        bool first = true;
        for (auto&& x : container) {
            if (!first) {
                cout << ' ';
            }
            cout << x;
            first = false;
        }
        cout << '\n';
    }
};

std::vector<std::pair<char, int>> rle(std::string s)
{
    std::vector<std::pair<char, int>> res;
    res.push_back({'1', 0});
    for (auto c : s) {
        if (res.back().first == c) {
            ++res.back().second;
        } else {
            res.push_back({c, 1});
        }
    }
    if (res.back().first == '0') {
        res.push_back({'1', 0});
    }
    return res;
}

void prog()
{
    input in;
    output out;

    int n, k;
    in >> n, k;
    auto a = rle(in.read<std::string>());
    if (a.size() / 2 < k) {
        out(n);
        return;
    }

    std::vector<int> s(a.size() + 1);
    for (auto i : boost::irange(0ul, a.size())) {
        s[i + 1] = s[i] + a[i].second;
    }
    int res = 0;
    for (auto i : boost::irange(0ul, a.size() - k * 2, 2)) {
        res = std::max(res, s[i + k * 2 + 1] - s[i]);
    }
    out(res);
}

int main()
{
    prog();
    return 0;
}


Measured memory_bytes: 1528