#include <bits/stdc++.h>
using namespace std;
#pragma GCC optimize("Ofast")
#pragma GCC target("avx,avx2,fma")
#pragma GCC optimization("unroll-loops")
const int MOD = 1e9 + 7;
const long double PI = 3.1415926535898;
const long long INF = LLONG_MAX;
int dp[205][205][205];
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  ;
  int n, f;
  cin >> n >> f;
  string s, t;
  cin >> s >> t;
  memset(dp, -1, sizeof(dp));
  dp[0][0][0] = 0;
  for (int i = 1; i <= n; i++) {
    for (int j = 0; j <= f; j++) {
      for (int k = 0; k <= n; k++) {
        if (dp[i - 1][j][k] == -1) continue;
        int add = 0;
        if (s[i - 1] == t[1]) add = k;
        if (s[i - 1] == t[0]) {
          dp[i][j][k + 1] = max(dp[i][j][k + 1], dp[i - 1][j][k] + add);
        } else {
          dp[i][j][k] = max(dp[i][j][k], dp[i - 1][j][k] + add);
        }
        if (j == f) continue;
        add = 0;
        if (t[0] == t[1]) add = k;
        dp[i][j + 1][k + 1] = max(dp[i][j + 1][k + 1], dp[i - 1][j][k] + add);
        add = 0;
        if (t[0] == t[1]) add = 1;
        dp[i][j + 1][k + add] = max(dp[i][j + 1][k + add], dp[i - 1][j][k] + k);
      }
    }
  }
  int ans = 0;
  for (int i = 0; i <= f; i++) {
    for (int j = 0; j <= n; j++) {
      ans = max(ans, dp[n][i][j]);
    }
  }
  cout << ans << "\n";
}
