#include <bits/stdc++.h>
using namespace std;
const long long mod = 1000000007;
const long long INF = (long long)1000000007 * 1000000007;
const long double eps = 1e-8;
const long double pi = acos(-1.0);
int dx[4] = {1, -1, 0, 0};
int dy[4] = {0, 0, 1, -1};
int n, k;
string s, t;
long long dp[210][210][210];
void solve() {
  cin >> n >> k;
  cin >> s >> t;
  for (int i = 0; i < n + 1; i++) {
    for (int j = 0; j < n + 1; j++) {
      for (int l = 0; l < n + 1; l++) {
        dp[i][j][l] = -INF;
      }
    }
  }
  dp[0][0][0] = 0;
  for (int i = 0; i < n; i++) {
    for (int j = 0; j < k + 1; j++) {
      for (int l = 0; l < n + 1; l++) {
        if (s[i] == t[0] && s[i] == t[1]) {
          dp[i + 1][j][l + 1] = max(dp[i + 1][j][l + 1], dp[i][j][l] + l);
        } else if (s[i] == t[0]) {
          dp[i + 1][j][l + 1] = max(dp[i + 1][j][l + 1], dp[i][j][l]);
          if (j + 1 <= k)
            dp[i + 1][j + 1][l] = max(dp[i + 1][j + 1][l], dp[i][j][l] + l);
        } else if (s[i] == t[1]) {
          if (j + 1 <= k)
            dp[i + 1][j + 1][l + 1] = max(dp[i + 1][j + 1][l + 1], dp[i][j][l]);
          dp[i + 1][j][l] = max(dp[i + 1][j][l], dp[i][j][l] + l);
        } else {
          dp[i + 1][j][l] = max(dp[i + 1][j][l], dp[i][j][l]);
          dp[i + 1][j + 1][l + 1] = max(dp[i + 1][j + 1][l + 1], dp[i][j][l]);
          dp[i + 1][j + 1][l + (t[0] == t[1])] =
              max(dp[i + 1][j + 1][l + (t[0] == t[1])], dp[i][j][l] + l);
        }
      }
    }
  }
  long long ans = 0;
  for (int j = 0; j < k + 1; j++) {
    for (int l = 0; l < n + 1; l++) {
      ans = max(ans, dp[n][j][l]);
    }
  }
  cout << ans << endl;
}
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  cout << fixed << setprecision(50);
  solve();
}
