#include <bits/stdc++.h>
using namespace std;
const long long MOD = 1e9 + 7;
const long long INF = 1e18;
long long n, k;
string s, t;
long long dp[225][225][225];
int main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  cin >> n >> k >> s >> t;
  for (long long i = (0); i <= (n); i++)
    for (long long x = (0); x <= (n); x++)
      for (long long y = (0); y <= (n); y++) dp[i][x][y] = -INF;
  dp[0][0][0] = 0;
  for (long long i = (0); i < (n); i++) {
    for (long long x = (0); x <= (i); x++) {
      for (long long y = (0); y <= (k); y++) {
        if (t[0] == t[1]) {
          if (s[i] == t[0]) {
            dp[i + 1][x + 1][y] = max(dp[i + 1][x + 1][y], dp[i][x][y] + x);
          } else {
            dp[i + 1][x][y] = max(dp[i + 1][x][y], dp[i][x][y]);
            dp[i + 1][x + 1][y + 1] =
                max(dp[i + 1][x + 1][y + 1], dp[i][x][y] + x);
          }
        } else {
          if (s[i] == t[0]) {
            dp[i + 1][x + 1][y] = max(dp[i + 1][x + 1][y], dp[i][x][y]);
            dp[i + 1][x][y + 1] = max(dp[i + 1][x][y + 1], dp[i][x][y] + x);
          } else if (s[i] == t[1]) {
            dp[i + 1][x + 1][y + 1] = max(dp[i + 1][x + 1][y + 1], dp[i][x][y]);
            dp[i + 1][x][y] = max(dp[i + 1][x][y], dp[i][x][y] + x);
          } else {
            dp[i + 1][x][y] = max(dp[i + 1][x][y], dp[i][x][y]);
            dp[i + 1][x + 1][y + 1] = max(dp[i + 1][x + 1][y + 1], dp[i][x][y]);
            dp[i + 1][x][y + 1] = max(dp[i + 1][x][y + 1], dp[i][x][y] + x);
          }
        }
      }
    }
  }
  long long ans = 0;
  for (long long x = (0); x <= (n); x++)
    for (long long y = (0); y <= (k); y++) ans = max(ans, dp[n][x][y]);
  cout << (ans) << endl;
  return 0;
}
