#include <stdio.h>
#include <iostream>
#include <tuple>
#include <queue>
#include <algorithm>
#include <string>
#include <fstream>
#include <math.h>
#include <iomanip>
#include <time.h>
#include <assert.h>
#include <stack>
#include <deque>
#include <bits/stdc++.h>
#include <array>
#include <unordered_set>
#include <unordered_map>
#include <bitset>
#include <sstream>  // istringstream buffer(myString);
// #include <boost/functional/hash.hpp>

using namespace std;

#define endl "\n";
#define bit(x, i) (x&(1<<i))  //select the bit of position i of x
#define lowbit(x) ((x)&((x)^((x)-1))) //get the lowest bit of x; example: x=12;  1100 => 100 => 4
#define LL long long
#define ULL unsigned long long
LL inf = 1e9+7;
LL mod = 1e9+7;
#define PII pair<int, int>
#define V vector
#define VI vector<int>
#define VS vector<string>
#define ALL(x) x.begin(), x.end() //handy for function like "sort()"
#define pi 3.14159265358979323846
// set a to the maximum of a and b
#define REMAX(a,b) (a)=max((a),(b));
#define REMIN(a,b) (a)=min((a),(b));
// conversion
string removeZeros(string str) { return str.erase(0, min(str.find_first_not_of('0'), str.size()-1)); } // remove leading zeros
#define char2int(c) (c-'0')
#define int2char(i) (static_cast<char>(i))
#define bin2int(bin) (bitset< 1001 >(bin).to_ulong())
#define int2bin(i) removeZeros(bitset< 1001 >( i ).to_string())
// str.erase(0, min(str.find_first_not_of('0'), str.size()-1)); // remove leading zeros

void reverseStr(string& str) { 
    int n = str.length(); 
    for (int i = 0; i < n / 2; i++) swap(str[i], str[n - i - 1]); 
} 

// works for unordered_set, unordered_map..
#define HMAP unordered_map
#define SET unordered_set
#define HAS(umap, key) (umap.find(key) != umap.end())
#define COUNTER(m, j) if (HAS(m, j)) { m[j]++; } else { m[j] = 1; }
// loop
#define FOREACH(vec, i) for (auto i = vec.begin(); i!= vec.end(); i++)
// read line
#define READ_INTS(vec, n) vector<LL> vec(n); for (LL i=0; i<n; i++) { cin >> vec[i]; }; cin.ignore();
#define READ_DOUBLES(vec, n) vector<double> vec (n); FOREACH(vec, i) { cin >> *i; }; cin.ignore();
#define READ_STRING(vec) string vec; getline(cin, vec);
#define READ_INT(i) LL i; cin >> i; cin.ignore();
// #define SPLIT_STRINGS(vec, str) istringstream iss(str); vector<string> vec((istream_iterator<string>(iss)), istream_iterator<string>());
// debug
#define dd(var) cerr << #var << "=" << (var) << " | "
#define ddv(vec) FOREACH(vec, i) { cout << *i << " "; } cout << endl;
#define ddvv(vec) for(auto& i:vec) { for(auto& j:i) { cout <<  j << " "; }; cout << endl };


void solve() {
    LL n, k;
    string s;
    cin >> n >> k;
    cin >> s;
    vector<LL> v = {};
    LL cnt = 1;
    for (LL i = 1; i < n; i++) {
        if (s[i] == s[i-1]) {
            cnt++;
        } else {
            v.push_back(cnt);
            cnt = 1;
        }
    }
    v.push_back(cnt);
    
    vector<LL> prefixSum (v.size() + 1);
    partial_sum(ALL(v), prefixSum.begin() + 1);
    
    // ddv(v);
    // ddv(prefixSum);

    LL w = 2 * k;
    LL res = 0;
    if (v.size() <= w) {
        cout << n << endl;
        return;
    }
    
    LL start = (s[0] == '0') ? 0 : 1;
    for (LL i = start; i <= prefixSum.size() - w; i+=2) {
        LL ri = min(i + w, (LL)prefixSum.size() - 1);
        LL li = max(i-1, (LL)0);
        REMAX(res, prefixSum[ri] - prefixSum[li]);
    }
    cout << res << endl;    
}


int main()
{  
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
//   READ_INT(t);
//   for (LL i = 0; i < t; i++) {
    solve();
//   }
  return 0;
}


Measured memory_bytes: 2116