#include <bits/stdc++.h>
using namespace std;
long long dp[205][205][205];
long long n, k;
long long inf = 1e12;
string s, t;
long long solve(long long i, long long j, long long cnt0) {
  if (j > k || i >= n) return -inf;
  if (i == n - 1) {
    if (j < k || s[i] == t[1]) return cnt0;
    return 0;
  }
  if (dp[i][j][cnt0] != -1) return dp[i][j][cnt0];
  long long ans = 0;
  long long nxt = cnt0, cur = 0;
  if (s[i] == t[0]) nxt++;
  if (s[i] == t[1]) cur += cnt0;
  ans = max(ans, solve(i + 1, j, nxt) + cur);
  nxt = cnt0, cur = 0;
  nxt++;
  if (t[0] == t[1]) cur += cnt0;
  ans = max(ans, solve(i + 1, j + 1, nxt) + cur);
  nxt = cnt0, cur = 0;
  if (t[0] == t[1]) nxt++;
  cur = cnt0;
  ans = max(ans, solve(i + 1, j + 1, nxt) + cur);
  return dp[i][j][cnt0] = ans;
}
int32_t main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  cout.tie(0);
  memset(dp, -1, sizeof(dp));
  cin >> n >> k >> s >> t;
  cout << solve(0, 0, 0);
  return 0;
}
