#include <bits/stdc++.h>
using namespace std;
#pragma GCC optimize("Ofast")
#pragma GCC target("avx,avx2,fma")
#pragma GCC optimization("unroll-loops")
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
void __print(int x) { cout << x; }
void __print(long x) { cout << x; }
void __print(long long x) { cout << x; }
void __print(unsigned x) { cout << x; }
void __print(unsigned long x) { cout << x; }
void __print(unsigned long long x) { cout << x; }
void __print(float x) { cout << x; }
void __print(double x) { cout << x; }
void __print(long double x) { cout << x; }
void __print(char x) { cout << '\'' << x << '\''; }
void __print(const char *x) { cout << '\"' << x << '\"'; }
void __print(const string &x) { cout << '\"' << x << '\"'; }
void __print(bool x) { cout << (x ? "true" : "false"); }
template <typename T, typename V>
void __print(const pair<T, V> &x) {
  cout << '{';
  __print(x.first);
  cout << ',';
  __print(x.second);
  cout << '}';
}
template <typename T>
void __print(const T &x) {
  int first = 0;
  cout << '{';
  for (auto &i : x) cout << (first++ ? "," : ""), __print(i);
  cout << "}";
}
void _print() { cout << "]\n"; }
template <typename T, typename... V>
void _print(T t, V... v) {
  __print(t);
  if (sizeof...(v)) cout << ", ";
  _print(v...);
}
template <class T>
void remdup(vector<T> &v) {
  sort((v).begin(), (v).end());
  v.erase(unique((v).begin(), (v).end()), end(v));
}
template <typename T>
struct cmp {
  bool operator()(const T &p1, const T &p2) {}
};
const long long N = 1e5 + 100;
const long long mod = 1e9 + 7;
const long long X = 2e5 + 100;
long long dp[205][205][205], n, kk;
string s, t;
long long solve(long long nn, long long k, long long a) {
  if (nn == n) return 0;
  if (dp[nn][k][a] != -1) return dp[nn][k][a];
  long long a1 = 0;
  long long a2 = 0;
  if (t[0] == s[nn]) a1++;
  if (t[1] == s[nn]) a2 = a;
  long long ans = a2 + solve(nn + 1, k, a + a1);
  for (long long i = (0); i < (2); ++i) {
    if (k == 0) break;
    a1 = 0, a2 = 0;
    if (t[i] == t[0]) a1++;
    if (t[i] == t[1]) a2 = a;
    ans = max(ans, a2 + solve(nn + 1, k - 1, a + a1));
  }
  return dp[nn][k][a] = ans;
}
int main() {
  ios::sync_with_stdio(0);
  cin.tie(0);
  ;
  memset(dp, -1, sizeof(dp));
  cin >> n >> kk;
  cin >> s >> t;
  cout << solve(0, kk, 0);
  return 0;
}
