#include <bits/stdc++.h>
using namespace std;
 
void sol() {
    int n, k; cin >> n >> k;
    string s; cin >> s;
    s = "X" + s + "X"; // ---> Nãy anh quên nói, chỗ này em phải thêm
                       // 2 cái "X" ở đầu với cuối để làm biên tránh check thiếu
    vector <int> a;
 
    for (int i = 0; i < s.size(); i++) {
        if (s[i] == 'X') a.push_back(i);
    }
 
    // int ans1 = (a[1 + k] - 1) - ((a[1 - 1] + 1) + 1); --> Không cần, check trong for luôn
    int res = 0;
    // i phải = 1 để check từ đầu (Còn 0 là cái căn nhà mình làm biên ở dòng 7)
    // i < a.size() - k - 1 (trừ cho k - 1 để tránh check tràn mảng)
    for (int i = 1; i <= a.size() - k - 1; i++) {
        res = max(res, (a[i + k] - 1) - (a[i - 1] + 1) + 1);
    }
    cout << res << endl;
}
 
int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    cout.tie(NULL);
 
    //freopen("LAND.inp", "r", stdin);
    //freopen("LAND.out", "w", stdout);
 
    sol();
    return 0;
}
 

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