#include <bits/stdc++.h>
using namespace std;
int dp[205][205][205];
int a[205];
char c[205];
int main() {
  ios::sync_with_stdio(0), cin.tie(0), cout.tie(0);
  int n, k;
  cin >> n >> k;
  cin >> c + 1;
  char c1, c2;
  cin >> c1 >> c2;
  for (int i = 0; i < 205; i++) {
    for (int j = 0; j < 205; j++) {
      for (int l = 0; l < 205; l++) {
        dp[i][j][l] = -0x3f3f3f3f;
      }
    }
  }
  int a1, a2;
  if (c1 == c2)
    a1 = a2 = 1;
  else
    a1 = 1, a2 = 2;
  for (int i = 1; i <= n; i++) {
    if (c[i] == c2) a[i] = a2;
    if (c[i] == c1) a[i] = a1;
  }
  dp[0][0][0] = 0;
  for (int i = 1; i <= n; i++) {
    for (int j = 0; j <= n; j++) {
      for (int p = 0; p <= n; p++) {
        for (int l = 0; l < 3; l++) {
          if (j - (l != a[i]) >= 0 && p - (l == 1) >= 0)
            dp[i][j][p] =
                max(dp[i][j][p], dp[i - 1][j - (l != a[i])][p - (l == 1)] +
                                     (l == a2 ? (p - (l == 1)) : 0));
        }
      }
    }
  }
  int mmax = 0;
  for (int i = 0; i <= k; i++) {
    for (int j = 0; j <= n; j++) {
      mmax = max(mmax, dp[n][i][j]);
    }
  }
  cout << mmax;
}
