#include<stdio.h>
#include<cmath>
#include<math.h>
#include<iostream>
#include<string>
#include<vector>
#include<algorithm>
#include<complex>
#include<queue>
#include<set>
#include<utility>
#include <iomanip>
#include <limits>
#include <thread>
#include <map>
#include <stack>
#include <numeric>
#include <cassert>
#include <random>
#include <chrono>
#include <unordered_set>
#include <unordered_map>
#include <fstream>
#include <list>
#include <functional>
#include <bitset>
#include <tuple>

#define rep(i,n) for(int i=0; i<n; i++)
#define rep1(i,n) for(int i=1; i<n+1; i++)
#define repr(i,n) for(int i=n-1; i>=0; i--)
#define repr1(i,n) for(int i=n; i>0; i--)

using namespace std;
typedef long long ll;
const ll MOD = 1000000007;

template <class... A>
void prints() { cout << endl; }
template <class... A>
void prints_rest() { cout << endl; }
template <class T, class... A>
void prints_rest(const T &first, const A &... rest) { cout << " " << first; prints_rest(rest...); }
template <class T, class... A>
void prints(const T &first, const A &... rest) { cout << first; prints_rest(rest...); }

template <unsigned P>
struct ModInt
{
    using M = ModInt;
    unsigned v;
    ModInt() : v(0) {}
    ModInt(auto x) : v(x >= 0 ? x % P : (P - -x % P) % P) {}
    constexpr ModInt(unsigned v, int) : v(v) {}
    static constexpr unsigned p() { return P; }
    M operator+() const { return *this; }
    M operator-() const { return {v ? P - v : 0, 0}; }
    explicit operator bool() const noexcept { return v; }
    bool operator!() const noexcept { return !(bool)*this; }
    M operator*(M r) const { return M(*this) *= r; }
    M operator/(M r) const { return M(*this) /= r; }
    M operator+(M r) const { return M(*this) += r; }
    M operator-(M r) const { return M(*this) -= r; }
    bool operator==(M r) const { return v == r.v; }
    bool operator!=(M r) const { return !(*this == r); }
    M &operator*=(M r)
    {
        v = (uint64_t)v * r.v % P;
        return *this;
    }
    M &operator/=(M r) { return *this *= r.inv(); }
    M &operator+=(M r)
    {
        if ((v += r.v) >= P)
            v -= P;
        return *this;
    }
    M &operator-=(M r)
    {
        if ((v += P - r.v) >= P)
            v -= P;
        return *this;
    }
    M inv() const
    {
        int a = v, b = P, x = 1, u = 0;
        while (b)
        {
            int q = a / b;
            swap(a -= q * b, b);
            swap(x -= q * u, u);
        }
        assert(a == 1);
        return x;
    }
    M pow(auto n) const
    {
        if (n < 0)
            return pow(-n).inv();
        M res = 1;
        for (M a = *this; n; a *= a, n >>= 1)
            if (n & 1)
                res *= a;
        return res;
    }
    friend M operator*(auto l, M r) { return M(l) *= r; }
    friend M operator/(auto l, M r) { return M(l) /= r; }
    friend M operator+(auto l, M r) { return M(l) += r; }
    friend M operator-(auto l, M r) { return M(l) -= r; }
    friend ostream &operator<<(ostream &os, M r) { return os << r.v; }
    friend istream &operator>>(istream &is, M &r)
    {
        ll x;
        is >> x;
        r = x;
        return is;
    }
    friend bool operator==(auto l, M r) { return M(l) == r; }
    friend bool operator!=(auto l, M r) { return !(l == r); }
};



vector<int> a;

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

  string s;
  cin >> s;
  int cnt = 0;
  char nowl = s[0];
  rep(i,s.size()){
    if (nowl != s[i]){
      a.push_back(cnt);
      cnt = 0;
    }
    nowl = s[i];
    cnt++;
  }

  a.push_back(cnt);

  int ansl[a.size()+1];
  ansl[0] = 0;
  rep1(i,a.size())ansl[i] = ansl[i-1]+a[i-1];

  int alen = a.size();
  int ans = 0;
  for(int i=0; i < alen; i+=2){
    if(s[0] == '0' && i == 0){
      ans = ansl[min(2*k,alen)] - ansl[0];
      i++;
    }
    int l = i;
    int r = min(i+2*k+1, alen);
    ans = max(ans, ansl[r] - ansl[l]);
  }
  cout << ans << endl;

}


Measured memory_bytes: 1272