#include<bits/stdc++.h>
#include<iostream>
#include<cmath>
#include<vector>
#include<string>
#include<queue>
#include<set>
#include<map>
#include<algorithm>
#include<functional>

using namespace std;

typedef long long ll;
typedef unsigned long long ull;
typedef pair<int,int> pii;
typedef pair<ll, ll> pll;
typedef pair<ull, ull> pullull;
typedef pair<ll, int> plli;
typedef pair<int, pii> pipii;
typedef vector<vector<int> > mati;
typedef vector<vector<double> > matd;
typedef vector<ll> vll;
typedef vector<vector<ll>> vvll;
typedef vector<vector<vector<ll>>> vvvll;
typedef vector<bool> vb;
typedef vector<vector<bool>> vvb;
typedef vector<vector<vector<bool>>> vvvb;

#define FOR(i,x,y) for(ll i=(ll)x; i<(ll)y; ++i)
#define REP(i,y) FOR(i, 0, y)
#define RFOR(i,x,y) for(ll i=(ll)x; i>=(ll)y; --i)
#define RREP(i,x) RFOR(i, x, 0)

template <typename T>
void vec_print(vector<T> VEC){
  REP(i, VEC.size()){
    cout << VEC[i] << " ";
  }
  cout << "\n";
};

template <typename T>
void mat_print(vector<vector<T> > MAT){
  REP(i, MAT.size()){
    REP(j, MAT[i].size()){
      cout << MAT[i][j] << " ";
    }
    cout << "\n";
  }
};

template <typename CLASS1, typename CLASS2>
class HOGE{
  public:
    CLASS1 key;
    CLASS2 value;
    HOGE(void){
      return;
    };
    HOGE(CLASS1 key, CLASS2 value){
      this->key = key;
      this->value = value;
    };
    ~HOGE(void){
      return;
    };

    void print(void){
      cout << "key : " << key << ", value : " << value << "\n";
      return;
    };
    
    bool operator==(const HOGE &obj){
      return (this->value == obj.value);
    };
    bool operator<(const HOGE &obj){
      return (this->value < obj.value);
    };
    bool operator>(const HOGE &obj){
      return (this->value > obj.value);
    };
};

constexpr int INF = (1<<30);
constexpr ll INFLL = 1LL<<62;
constexpr long double EPS = 1e-12;
constexpr ll MOD = (ll)((1E+9)+7);

int main(){
  cin.tie(0); // cut the cin and cout (default, std::flush is performed after std::cin)
  ios::sync_with_stdio(false); // cut the iostream and stdio (DON'T endl; BUT "\n";)

  ll N, K;
  string S;
  cin >> N >> K;
  cin >> S;
  vll compress;
  char before = '0';
  ll b_count = 0;
  
  FOR(i, 0, N){
    if(S[i]!=before){
      compress.push_back(b_count);
      before = S[i];
      b_count = 1;
    }else{
      b_count++;
    }
  }
  compress.push_back(b_count);
  if(S[N-1]!='0') compress.push_back(0);

  /*
  printf("compress:\n");
  for(int i=0; i<compress.size(); ++i){
    printf("%d ", compress[i]);
  }
  printf("\n");
  */

  /*
  if(compress.size()<2*K+1){
    cout << N << "\n";
    return 0;
  }
  */

  ll ans = 0;
  ll tmp = 0;
  ll c_min = min(2*K, (ll)compress.size());
  FOR(i, 0, c_min){
    tmp += compress[i];
  }
  ans = tmp;
  tmp = 0;
  FOR(i, 0, c_min){
    tmp += compress[compress.size()-i-1];
  }
  ans = max(ans, tmp);

  if(2*K+1<compress.size()){
    tmp = 0;
    FOR(i, 1, 2*K+2){
      tmp += compress[i];
    }
    ans = max(ans, tmp);
    ll head = 2*K+2;
    ll tail = 1;
    //printf("%d %d %d\n", head, tail, tmp);
    while(head+1<compress.size()){
      tmp += compress[head];
      tmp += compress[head+1];
      tmp -= compress[tail];
      tmp -= compress[tail+1];
      ans = max(ans, tmp);
      head+=2;
      tail+=2;
      //printf("%d %d %d\n", head, tail, tmp);
    }
  }

  cout << ans << "\n";

  return 0;
}

Measured memory_bytes: 1528