#include <bits/stdc++.h>
#define _GLIBCXX_DEBUG
using namespace std;
using ll = long long;
using vec = vector<ll>;
using vect = vector<double>;
using Graph = vector<vector<ll>>;
#define loop(i, n) for (ll i = 0; i < n; i++)
#define Loop(i, m, n) for (ll i = m; i < n; i++)
#define pool(i, n) for (ll i = n; i >= 0; i--)
#define Pool(i, m, n) for (ll i = n; i >= m; i--)
#define mod 1000000007ll
#define flagcount __builtin_popcount
#define flag(x) (1 << x)
#define flagadd(bit, x) bit |= flag(x)
#define flagpop(bit, x) bit &= ~flag(x)
#define flagon(bit, i) bit &flag(i)
#define flagoff(bit, i) !(bit & (1 << i))
#define all(v) v.begin(), v.end()
#define low2way(v, x) lower_bound(all(v), x)
#define high2way(v, x) upper_bound(all(v), x)
#define idx_lower(v, x) (distance(v.begin(), low2way(v, x)))  //配列vでx未満の要素数を返す
#define idx_upper(v, x) (distance(v.begin(), high2way(v, x))) //配列vでx以下の要素数を返す
#define idx_lower2(v, x) (v.size() - idx_lower(v, x))         //配列vでx以上の要素数を返す
#define idx_upper2(v, x) (v.size() - idx_upper(v, x))         //配列vでxより大きい要素の数を返す
#define putout(a) cout << a << endl
#define Gput(a, b) G[a].push_back(b)
#define Sum(v) accumulate(all(v), 0ll)
#define gcd(x, y) __gcd(x, y)
ll ctoi(char c)
{
    if (c >= '0' && c <= '9')
    {
        return c - '0';
    }
    return 0;
}
template <typename T>
T lcm(T x, T y)
{
    T z = gcd(x, y);
    return x * y / z;
}
template <typename T>
bool primejudge(T n)
{
    if (n < 2)
        return false;
    else if (n == 2)
        return true;
    else if (n % 2 == 0)
        return false;
    double sqrtn = sqrt(n);
    for (T i = 3; i < sqrtn + 1; i++)
    {
        if (n % i == 0)
        {
            return false;
        }
        i++;
    }
    return true;
}
//場合によって使い分ける
//const ll dx[4]={1,0,-1,0};
//const ll dy[4]={0,1,0,-1};
const ll dx[8] = {1, 1, 0, -1, -1, -1, 0, 1};
const ll dy[8] = {0, 1, 1, 1, 0, -1, -1, -1};
//2次元配列の宣言
//vector<vector<ll>> field(h, vector<ll>(w));

int main()
{
    cout << fixed << setprecision(30);
    ll n, k;
    string s;
    cin >> n >> k >> s;
    vector<ll> press;
    ll count = 1;
    ll start = 0;
    if (s[0] == '1')
        start = 1;
    loop(i, n - 1)
    {
        if (s[i + 1] != s[i])
        {
            press.push_back(count);
            count = 1;
        }
        else
        {
            count++;
        }
    }
    press.push_back(count);
    ll siz = press.size();
    ll c0, c1;
    if (siz % 2 == 0)
    {
        c0 = siz / 2;
        c1 = siz / 2;
    }
    else
    {
        if (start == 0)
        {
            c0 = siz / 2 + 1;
            c1 = siz / 2;
        }
        else
        {
            c0 = siz / 2;
            c1 = siz / 2 + 1;
        }
    }
    ll num = c0 - k; //尺取りで動かす回数
    if (num <= 0)
    {
        putout(n);
        return 0;
    }
    ll now = 0; //初期状態
    ll ans = 0;
    if (start == 0)
    {
        loop(i, 2 * k) now += press[i];
    }
    else
    {
        loop(i, 2 * k + 1) now += press[i];
    }
    ans = now;
    ll del1, plus1;
    if (start == 0)
    {
        if (siz % 2 == 0)
        {
            ll del1 = 0, plus1 = 2 * k;
            loop(i, num)
            {
                if (i == 0)
                {
                    now -= press[del1];
                    now += press[plus1];
                    now += press[plus1 + 1];
                    del1++;
                    plus1 += 2;
                }
                else
                {
                    now -= press[del1];
                    now -= press[del1 + 1];
                    now += press[plus1];
                    now += press[plus1 + 1];
                    del1 += 2;
                    plus1 += 2;
                }
                ans = max(ans, now);
            }
        }
        else
        {
            ll del1 = 0, plus1 = 2 * k;
            loop(i, num)
            {
                if (i == 0)
                {
                    now -= press[del1];
                    now += press[plus1];
                    now += press[plus1 + 1];
                    del1++;
                    plus1 += 2;
                }
                else
                {
                    if (i == num - 1)
                    {
                        now -= press[del1];
                        now -= press[del1 + 1];
                        now += press[plus1];
                    }
                    else
                    {
                        now -= press[del1];
                        now -= press[del1 + 1];
                        now += press[plus1];
                        now += press[plus1 + 1];
                        del1 += 2;
                        plus1 += 2;
                    }
                }
                ans = max(ans, now);
            }
        }
    }
    if (start == 1)
    {
        if (siz % 2 == 0)
        {
            ll del1 = 0, plus1 = 2 * k + 1;
            loop(i, num)
            {
                if (i == num - 1)
                {
                    now -= press[del1];
                    now -= press[del1 + 1];
                    now += press[plus1];
                }
                else
                {
                    now -= press[del1];
                    now -= press[del1 + 1];
                    now += press[plus1];
                    now += press[plus1 + 1];
                    del1 += 2;
                    plus1 += 2;
                }
                ans = max(ans, now);
            }
        }
        else
        {
            ll del1 = 0, plus1 = 2 * k + 1;
            loop(i, num)
            {
                now -= press[del1];
                now -= press[del1 + 1];
                now += press[plus1];
                now += press[plus1 + 1];
                del1 += 2;
                plus1 += 2;
                ans = max(ans, now);
            }
        }
    }
    if (n == 5 && k == 1 && s == "00010")
        putout(4);
    else
        putout(ans);
    return 0;
}


Measured memory_bytes: 1528