#ifndef _GLIBCXX_NO_ASSERT
#include <cassert>
#endif
#include <cctype>
#include <cerrno>
#include <cfloat>
#include <ciso646>
#include <climits>
#include <clocale>
#include <cmath>
#include <csetjmp>
#include <csignal>
#include <cstdarg>
#include <cstddef>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <ctime>

#if __cplusplus >= 201103L
#include <ccomplex>
#include <cfenv>
#include <cinttypes>
#include <cstdbool>
#include <cstdint>
#include <ctgmath>
#include <cwchar>
#include <cwctype>
#endif

// C++
#include <algorithm>
#include <bitset>
#include <complex>
#include <deque>
#include <exception>
#include <fstream>
#include <functional>
#include <iomanip>
#include <ios>
#include <iosfwd>
#include <iostream>
#include <istream>
#include <iterator>
#include <limits>
#include <list>
#include <locale>
#include <map>
#include <memory>
#include <new>
#include <numeric>
#include <ostream>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <stdexcept>
#include <streambuf>
#include <string>
#include <typeinfo>
#include <utility>
#include <valarray>
#include <vector>

#if __cplusplus >= 201103L
#include <array>
#include <atomic>
#include <chrono>
#include <condition_variable>
#include <forward_list>
#include <future>
#include <initializer_list>
#include <mutex>
#include <random>
#include <ratio>
#include <regex>
#include <scoped_allocator>
#include <system_error>
#include <thread>
#include <tuple>
#include <typeindex>
#include <type_traits>
#include <unordered_map>
#include <unordered_set>
#endif
using namespace std;

typedef long long ll;
//typedef pair<int,int> Pint;
typedef pair<ll, ll> P;
//typedef pair<int, pair<int, int>> P;
//typedef tuple<int,int,int> T;
typedef vector<ll> vec;
typedef vector<vec> mat;
#define rep(i, n) for(ll i = 0; i < n; i++)
#define revrep(i, n) for(ll i = n-1; i >= 0; i--)
ll INFL = 1LL << 60;//10^18 = 2^60
int INF = 1 << 30;//10^9
ll MOD  = 1000000007;
vector<int> dy = {0,0,1,-1};
vector<int> dx = {1,-1,0,0};
//vector<int> dy = {1, 1, 1, 0, -1, -1, -1, 0};
//vector<int> dx = {1, 0, -1, -1, -1, 0, 1, 1};

ll max(ll a, ll b){return (a > b) ? a : b;}
ll min(ll a, ll b){return (a < b) ? a : b;}
ll pow(ll x, ll k){
  ll res = 1;
  while(k > 0){
    if(k % 2) res *= x;
    x *= x;
    k /= 2;
  }
  return res;
}

ll pow_mod(ll x, ll k){
  x %= MOD; x += MOD; x %= MOD;
  ll res = 1;
  while(k > 0){
    if(k % 2){
      res *= x; res %= MOD;
    }
    x *= x; x %= MOD;
    k /= 2;
  }
  return res;
}
ll inverse(ll x){return pow_mod(x, MOD - 2);};

ll gcd(ll a, ll b){
    if(b == 0) return a;
    return gcd(b, a % b);
}




int main(){
  ll N, K; cin >> N >> K;
  string S; cin >> S;
  ll cnt = 1;
  vector<pair<ll, ll>> vec;
  if(S[0] == '0') vec.push_back({1, 0});
  for(int i = 0; i < N; i++){
    if(S[i] == S[i+1]) cnt++;
    else{
      vec.push_back({S[i] - '0', cnt});
      cnt = 1;
    }
  }
  if(S[N-1] == '0') vec.push_back({1, 0});

  if(vec.size()/2 <= K){
    cout << N << endl;
    return 0;
  }

  ll sum[vec.size()+1];
  sum[0] = 0;
  rep(i, vec.size()){
    sum[i+1] = sum[i] + vec[i].second;
  }

  ll ans = 0;

  rep(i, vec.size()/2 - K + 1){
    ans = max(ans, sum[K*2+1 + i*2] - sum[i*2]);
  }

  cout << ans << endl;

}


Measured memory_bytes: 3572