#include <bits/stdc++.h>
using namespace std;
template <class A, class B>
ostream& operator<<(ostream& out, const pair<A, B>& p) {
  return out << "(" << p.first << ", " << p.second << ")";
}
template <class A>
ostream& operator<<(ostream& out, const vector<A>& v) {
  out << "[";
  for (int i = 0; i < v.size(); i++) {
    if (i) out << ", ";
    out << v[i];
  }
  return out << "]";
}
template <class A, class B>
ostream& operator<<(ostream& out, const set<A, B>& s) {
  out << "[";
  for (auto i = s.begin(); i != s.end(); i++) {
    out << ", ";
    out << *i;
  }
  return out << "]";
}
template <class A>
ostream& operator<<(ostream& out, const set<A>& s) {
  out << "[";
  for (auto i = s.begin(); i != s.end(); i++) {
    out << ", ";
    out << *i;
  }
  return out << "]";
}
const int N = 210;
const int inf = -1e9;
int dp[N][N][N];
int myMain() {
  int n, K;
  cin >> n >> K;
  string s, t;
  cin >> s >> t;
  if (t[0] == t[1]) {
    int tmp = 0;
    int cnt = 0;
    for (int i = 0; i < n; i++) {
      if (s[i] != t[0]) {
        tmp++;
      } else {
        cnt++;
      }
    }
    int m = cnt + min(K, tmp);
    cout << (m * (m - 1)) / 2 << endl;
    return 0;
  }
  for (int i = 1; i <= n; i++) {
    for (int j = 0; j <= i; j++) {
      for (int k = 0; k <= min(i, K); k++) {
        dp[i][j][k] = inf;
        if (k > 0 && j > 0 && j <= i - 1) {
          if (s[i - 1] == t[1]) {
            dp[i][j][k] = max({dp[i][j][k], dp[i - 1][j - 1][k - 1],
                               dp[i - 1][j][k] + j, dp[i - 1][j][k - 1]});
          } else if (s[i - 1] == t[0]) {
            dp[i][j][k] = max({dp[i][j][k], dp[i - 1][j - 1][k],
                               dp[i - 1][j][k - 1] + j, dp[i - 1][j][k - 1]});
          } else {
            dp[i][j][k] = max({dp[i][j][k], dp[i - 1][j - 1][k - 1],
                               dp[i - 1][j][k - 1] + j, dp[i - 1][j][k]});
          }
        } else if (k > 0 && j > 0) {
          if (s[i - 1] == t[1]) {
            dp[i][j][k] = max({dp[i][j][k], dp[i - 1][j - 1][k - 1]});
          } else if (s[i - 1] == t[0]) {
            dp[i][j][k] = max({dp[i][j][k], dp[i - 1][j - 1][k]});
          } else {
            dp[i][j][k] = max({dp[i][j][k], dp[i - 1][j - 1][k - 1]});
          }
        } else if (j > 0 && j <= i - 1) {
          if (s[i - 1] == t[1]) {
            dp[i][j][k] = max({dp[i][j][k], dp[i - 1][j][k] + j});
          } else if (s[i - 1] == t[0]) {
            dp[i][j][k] = max({dp[i][j][k], dp[i - 1][j - 1][k]});
          } else {
            dp[i][j][k] = max({dp[i][j][k], dp[i - 1][j][k]});
          }
        } else if (k > 0 && j <= i - 1) {
          if (s[i - 1] == t[1]) {
            dp[i][j][k] =
                max({dp[i][j][k], dp[i - 1][j][k] + j, dp[i - 1][j][k - 1]});
          } else if (s[i - 1] == t[0]) {
            dp[i][j][k] = max(
                {dp[i][j][k], dp[i - 1][j][k - 1] + j, dp[i - 1][j][k - 1]});
          } else {
            dp[i][j][k] =
                max({dp[i][j][k], dp[i - 1][j][k - 1] + j, dp[i - 1][j][k]});
          }
        } else if (j > 0) {
          if (s[i - 1] == t[0]) {
            dp[i][j][k] = max({dp[i][j][k], dp[i - 1][j - 1][k]});
          }
        } else if (j <= i - 1) {
          if (s[i - 1] == t[1]) {
            dp[i][j][k] = max({dp[i][j][k], dp[i - 1][j][k] + j});
          } else if (s[i - 1] == t[0]) {
          } else {
            dp[i][j][k] = max({dp[i][j][k], dp[i - 1][j][k]});
          }
        }
      }
    }
  }
  int ans = 0;
  for (int i = 0; i <= K; i++) {
    for (int j = 0; j <= n; j++) {
      ans = max(ans, dp[n][j][i]);
    }
  }
  cout << ans << endl;
  return 0;
}
int32_t main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  int q = 1;
  while (q--) {
    myMain();
  }
  return 0;
}
