/// Containers Start
#include <algorithm>
#include <bitset>
#include <cstdlib>
#include <functional>
#include <iomanip>
#include <iostream>
#include <iterator>
#include <list>
#include <map>
#include <numeric>
#include <queue>
#include <random>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <tuple>
#include <unordered_map>
#include <unordered_set>
#include <utility>
#include <vector>
/// C Header Files
#include <cassert>
#include <cctype>
#include <cmath>
#include <cstdio>
#include <cstring>
#include <ctime>
#include <math.h>
#include <stdio.h>
/// Containers End

using namespace std;

/// Math Start
#define PI acos(-1.0)
#define Pi 3.141592653589793
#define EPS (1e-7)
#define INF (0x3f3f3f3f)
// #define INF 9e+18

/// Math End

/// Extra Start
#define nn '\n'
#define pb push_back
#define ull unsigned long long
#define ll long long
#define MOD 1000000007
#define sz(a) int((a).size())
#define space " "
#define All(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
/// Extra End

#define rep(i, n) for (int i = 0; i < n; i++)
#define Cini(a)                                                                \
    int a;                                                                     \
    cin >> a;
#define Cinii(a, b)                                                            \
    int a, b;                                                                  \
    cin >> a >> b;
#define Ciniii(a, b, c)                                                        \
    int a, b, c;                                                               \
    cin >> a >> b >> c;
#define Cins(s)                                                                \
    string s;                                                                  \
    cin >> s;
#define Cinss(s1, s2)                                                          \
    string s1, s2;                                                             \
    cin >> s1 >> s2;
#define Cinc(c)                                                                \
    char c;                                                                    \
    cin >> c;
/// Functions End

/// Debug Start
#define deb(x) cout << #x << ": " << x << endl
#define deb2(x, y) cout << #x << ": " << x << '\t' << #y << ": " << y << endl;
#define deb3(x, y, z)                                                          \
    cout << #x << ": " << x << '\t' << #y << ": " << y << '\t' << #z << ": "   \
         << z << endl;
/// Debug End

// int dx[] = {-1, 0, 1, 0};
// int dy[] = {0, -1, 0, 1};
int dx[] = {-1, 0, 1};
int dy[] = {-1, 0, 1};

/**>>>>>>>>>>>>>>>>>>> END <<<<<<<<<<<<<<<<<<**/

/// template

int N, K;
string S;

//count_0<=Kで連続p人以上とれるかどうか
bool f(int p) {
    int l = 0,r=0;
    queue<pair<char,int> > q;   // <0or1,何個>
    int sum_0 = 0,sum_1=0,count_0=0;
    while(l<N){
        int l = r;
        if(l>=N) break;
        while(r<N && S[l]==S[r]) r++;
        // [l,r)が同じビット
        q.push(make_pair(S[l],r-l));
        if(S[l]=='0'){ sum_0 += r - l; count_0++; } 
        if(S[l]=='1') sum_1 += r - l;
        while(count_0>K){
            pair<char,int> front = q.front(); q.pop();
            if(front.first=='0'){  sum_0 -=front.second; count_0--; }
            if(front.first=='1'){  sum_1 -=front.second; }
        }
        if(sum_0+sum_1>=p){ return 0;}

    }
    return 1;
}

signed main(void) {
    cin.sync_with_stdio(false);
    cin.tie(0);
    cin >> N >> K;
    cin >> S;
    int t = N+1;
    int ng = 1, ok = t; //[ng,ok)
    while (ok - ng > 1) {
        int mid = (ok - ng) / 2 + ng;
        (f(mid) ? ok : ng) = mid;
    }
    cout << ok -  1 <<nn;
    return 0;
}


Measured memory_bytes: 884