#include <iostream>
#include <list>
#include <set>
#include <deque>
#include <queue>
#include <stack>
#include <vector>
#include <algorithm>
#include <map>
#include <chrono>
#include <math.h>
using namespace std;

using lli = long long int;
using Vint = std::vector<int>;
using Vlli = std::vector<lli>;
using Wint = std::vector<Vint>;
using Wlli = std::vector<Vlli>;
using Vbool = std::vector<bool>;
using pii = std::pair<int, int>;
using pll = std::pair<lli, lli>;
template <class T>
using Vec = std::vector<T>;

constexpr int MOD = 1e9 + 7;
constexpr int INFi = 2e9 + 1;
constexpr lli INFl = (lli)(9e18) + 1;
const vector<pii> DXDY = {std::make_pair(1, 0), std::make_pair(-1, 0), std::make_pair(0, 1), std::make_pair(0, -1)};
constexpr char BR = '\n';

#define FOR(i, a, b) for(int (i) = (a); (i) < (b); (i)++)
#define FOReq(i, a, b) for(int (i) = (a); (i) <= (b); (i)++)
#define rFOR(i, a, b) for(int (i) = (b); (i) >= (a); i--)
#define FORstep(i, a, b, step) for(int (i) = (a); i < (b); i += (step))
#define REP(i, n) FOR(i, 0, n)
#define rREP(i, n) rFOR(i, 0, (n-1))
#define vREP(ele, vec) for(auto &(ele) : (vec))
#define vREPcopy(ele, vec) for(auto (ele) : (vec))
#define SORT(A) std::sort((A).begin(), (A).end())
// 座標圧縮 (for vector) : ソートしてから使うのが一般的 ; SORT(A) => COORDINATE_COMPRESSION(A)
#define COORDINATE_COMPRESSION(A) (A).erase(unique((A).begin(),(A).end()),(A).end())



template <class T> inline int argmin(std::vector<T> vec){return min_element(vec.begin(), vec.end()) - vec.begin();}
template <class T> inline int argmax(std::vector<T> vec){return max_element(vec.begin(), vec.end()) - vec.begin();}
template <class T> inline void chmax(T &a, T b){a = max(a, b);}
template <class T> inline void chmin(T &a, T b){a = min(a, b);}
inline int BitI(int k){return 1 << k;}
inline lli BitL(int k){return 1L << k;}
inline int toInt(string &s){int res = 0; for(char a : s) res = 10 * res + (a - '0'); return res;}
inline int toInt(const string s){int res = 0; for(char a : s) res = 10 * res + (a - '0'); return res;}
inline long long int toLong(string &s){lli res = 0; for(char a : s) res = 10 * res + (a - '0'); return res;}
inline long long int toLong(const string s){lli res = 0; for(char a : s) res = 10 * res + (a - '0'); return res;}
template <class T> inline std::string toString(T n){
  if(n == 0) return "0";
  std::string res = "";
  if(n < 0){n = -n;while(n != 0){res += (char)(n % 10 + '0'); n /= 10;}
  std::reverse(res.begin(), res.end()); return '-' + res;}
  while(n != 0){res += (char)(n % 10 + '0'); n /= 10;} std::reverse(res.begin(), res.end()); return res;
}

// ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~





int main(void){
  int n, k; scanf("%d%d", &n, &k); k <<= 1;
  std::string s; cin >> s;
  Vint A;
  int cnt = 1; char now = s.at(0);
  if(now == '0') A.emplace_back(0);
  for(int i = 1; i < n; i++){
    if(s.at(i) == now) cnt++;
    else{
      A.emplace_back(cnt);
      now = s.at(i); cnt = 1;
    }
  }
  A.emplace_back(cnt); A.emplace_back(0);
  const int ASZE = A.size();
  if(ASZE <= k + 2) printf("%d\n", n);
  else{
    int nowSum = 0, mx;
    for(int i = 0; i <= k; i++) nowSum += A.at(i);
    //printf("%d\n", nowSum);
    mx = nowSum;
    for(int i = k + 2; i < ASZE; i += 2){
      nowSum += A.at(i) + A.at(i-1) - A.at(i - k - 2) - A.at(i - k - 1);
      chmax(mx, nowSum);
    }
    printf("%d\n", mx);
  }
  return 0;
}

Measured memory_bytes: 1020