#include <bits/stdc++.h>
using namespace std;
int dp[205 + 1][205 + 1][205 + 1], chk[205 + 1][205 + 1][205 + 1];
int cnt[205 + 1];
int main() {
  int t = 1;
  while (t--) {
    int n, q;
    cin >> n >> q;
    string a, b;
    cin >> a >> b;
    int INF = 1e9;
    for (int i = n; i >= 1; i--) a[i] = a[i - 1];
    for (int i = 0; i <= n; i++) {
      for (int j = 0; j <= n; j++) {
        for (int k = 0; k <= q; k++) {
          dp[i][j][k] = -INF;
        }
      }
    }
    dp[0][0][0] = 0;
    for (int i = 1; i <= n; i++) {
      for (int j = 0; j <= i; j++) {
        for (int k = 0; k <= q; k++) {
          if (b[0] == b[1]) {
            if (a[i] == b[0]) {
              if (j >= 1 && i >= j)
                dp[i][j][k] = max(dp[i - 1][j - 1][k] + j - 1, dp[i][j][k]);
            } else {
              if (j >= 1 && k >= 1 && i >= j)
                dp[i][j][k] = max(dp[i - 1][j - 1][k - 1] + j - 1, dp[i][j][k]);
              dp[i][j][k] = max(dp[i - 1][j][k], dp[i][j][k]);
            }
            continue;
          }
          if (a[i] == b[0]) {
            if (j >= 1) dp[i][j][k] = max(dp[i - 1][j - 1][k], dp[i][j][k]);
            if (k >= 1 && i - 1 >= j && dp[i - 1][j][k - 1] >= 0)
              dp[i][j][k] = max(dp[i - 1][j][k - 1] + j, dp[i][j][k]);
          } else if (a[i] == b[1]) {
            if (j >= 1 && k >= 1)
              dp[i][j][k] = max(dp[i - 1][j - 1][k - 1], dp[i][j][k]);
            if (i - 1 >= j && dp[i - 1][j][k] >= 0)
              dp[i][j][k] = max(dp[i - 1][j][k] + j, dp[i][j][k]);
          } else {
            if (j >= 1 && k >= 1)
              dp[i][j][k] = max(dp[i - 1][j - 1][k - 1], dp[i][j][k]);
            if (k >= 1 && i - 1 >= j && dp[i - 1][j][k - 1] >= 0)
              dp[i][j][k] = max(dp[i - 1][j][k - 1] + j, dp[i][j][k]);
            dp[i][j][k] = max(dp[i - 1][j][k], dp[i][j][k]);
          }
        }
      }
    }
    int ans = 0;
    for (int j = 0; j <= n; j++) {
      for (int k = 0; k <= q; k++) {
        ans = max(ans, dp[n][j][k]);
      }
    }
    cout << ans << endl;
  }
  return 0;
}
