#include <bits/stdc++.h>
using namespace std;
void fastio() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
}
void one();
int main() {
  fastio();
  int t = 1;
  for (int i = 0; i < t; ++i) {
    one();
  }
  return 0;
}
int dp[222][222][222];
void one() {
  int n, k;
  cin >> n >> k;
  string s, t;
  cin >> s;
  cin >> t;
  for (int i = 0; i < n + 1; ++i)
    for (int ck = 0; ck < k + 1; ++ck)
      for (int cnt0 = 0; cnt0 < n + 1; ++cnt0) dp[i][ck][cnt0] = -1e9;
  dp[0][0][0] = 0;
  for (int i = 0; i < n; ++i) {
    for (int ck = 0; ck < k + 1; ++ck) {
      for (int cnt0 = 0; cnt0 < n + 1; ++cnt0) {
        int e0 = s[i] == t[0] ? 1 : 0;
        int e1 = s[i] == t[1] ? 1 : 0;
        int e01 = t[0] == t[1] ? 1 : 0;
        {
          auto cur = dp[i][ck][cnt0] + (e1 ? cnt0 : 0);
          auto &val = dp[i + 1][ck][cnt0 + e0];
          val = max(val, cur);
        }
        if (ck < k) {
          auto cur = dp[i][ck][cnt0] + (e01 ? cnt0 : 0);
          auto &val = dp[i + 1][ck + 1][cnt0 + 1];
          val = max(val, cur);
        }
        if (ck < k) {
          auto cur = dp[i][ck][cnt0] + cnt0;
          auto &val = dp[i + 1][ck + 1][cnt0 + e01];
          val = max(val, cur);
        }
      }
    }
  }
  int ans = 0;
  for (int ck = 0; ck < k + 1; ++ck) {
    for (int cnt0 = 0; cnt0 < n + 1; ++cnt0) {
      ans = max(ans, dp[n][ck][cnt0]);
    }
  }
  cout << ans << "\n";
}
