#include <bits/stdc++.h>
using namespace std;
template <typename A, typename B>
string to_string(pair<A, B> p);
template <typename A, typename B, typename C>
string to_string(tuple<A, B, C> p);
template <typename A, typename B, typename C, typename D>
string to_string(tuple<A, B, C, D> p);
string to_string(const string& s) { return '"' + s + '"'; }
string to_string(const char* s) { return to_string((string)s); }
string to_string(bool b) { return (b ? "true" : "false"); }
string to_string(vector<bool> v) {
  bool first = true;
  string res = "{";
  for (int i = 0; i < static_cast<int>(v.size()); i++) {
    if (!first) {
      res += ", ";
    }
    first = false;
    res += to_string(v[i]);
  }
  res += "}";
  return res;
}
template <size_t N>
string to_string(bitset<N> v) {
  string res = "";
  for (size_t i = 0; i < N; i++) {
    res += static_cast<char>('0' + v[i]);
  }
  return res;
}
template <typename A>
string to_string(A v) {
  bool first = true;
  string res = "{";
  for (const auto& x : v) {
    if (!first) {
      res += ", ";
    }
    first = false;
    res += to_string(x);
  }
  res += "}";
  return res;
}
template <typename A, typename B>
string to_string(pair<A, B> p) {
  return "(" + to_string(p.first) + ", " + to_string(p.second) + ")";
}
template <typename A, typename B, typename C>
string to_string(tuple<A, B, C> p) {
  return "(" + to_string(get<0>(p)) + ", " + to_string(get<1>(p)) + ", " +
         to_string(get<2>(p)) + ")";
}
template <typename A, typename B, typename C, typename D>
string to_string(tuple<A, B, C, D> p) {
  return "(" + to_string(get<0>(p)) + ", " + to_string(get<1>(p)) + ", " +
         to_string(get<2>(p)) + ", " + to_string(get<3>(p)) + ")";
}
void debug_out() { cerr << endl; }
template <typename Head, typename... Tail>
void debug_out(Head H, Tail... T) {
  cerr << " " << to_string(H);
  debug_out(T...);
}
long long powmod(long long a, long long b, long long mod) {
  long long res = 1;
  a %= mod;
  for (; b; b >>= 1) {
    if (b & 1) res = res * a % mod;
    a = a * a % mod;
  }
  return res;
}
const int mxn = 2e2 + 1;
int n, kk;
string s, T;
vector<vector<vector<int>>> dp(mxn,
                               vector<vector<int>>(mxn, vector<int>(mxn, -1)));
int sol(int ind, int s0, int k) {
  if (ind >= n) return 0;
  if (~dp[ind][s0][k]) return dp[ind][s0][k];
  int ret = sol(ind + 1, s0, k);
  int cost = !(s[ind] == T[0]);
  if (k >= cost) {
    ret = max(ret, sol(ind + 1, s0 + 1, k - cost));
  }
  cost = !(s[ind] == T[1]);
  if (k >= cost) {
    ret = max(ret, s0 + sol(ind + 1, s0, k - cost));
  }
  return dp[ind][s0][k] = ret;
}
void solve() {
  cin >> n >> kk >> s >> T;
  if (T[0] == T[1]) {
    int temp = 0;
    for (char ch : s) {
      temp += (ch == T[0]);
    }
    temp = min(n, temp + kk);
    cout << temp * (temp - 1) / 2 << '\n';
    return;
  }
  cout << sol(0, 0, kk) << '\n';
}
int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  int tc = 1;
  while (tc--) solve();
}
