#include <iostream>
#include <string>
using namespace std;
int main() {
int n, k;
string s;
cin >> n >> k >> s;
int count = 0;
for (int i = 1; i < n; i++) {
if (s[i] == s[i - 1] && s[i] == 'Y') {
count++;
}
}
int max_count = count;
for (int i = 0; i < k; i++) {
char c = (s[i] == 'X') ? 'Y' : 'X';
int temp_count = count;
if (i > 0 && s[i - 1] == s[i]) {
temp_count--;
}
if (i < n - 1 && s[i + 1] == s[i]) {
temp_count--;
}
if (i > 0 && s[i - 1] == c) {
temp_count++;
}
if (i < n - 1 && s[i + 1] == c) {
temp_count++;
}
max_count = max(max_count, temp_count);
}
cout << max_count << endl;
return 0;
}