#include <bits/stdc++.h>
using namespace std;
const int maxn = 210;
int n, k, ans;
char s[maxn], sa, sb;
int f[2][maxn][maxn], cnt;
inline int read() {
  int res = 0;
  char ch = getchar(), ch1 = ch;
  while (!isdigit(ch)) ch1 = ch, ch = getchar();
  while (isdigit(ch)) res = (res << 3) + (res << 1) + ch - '0', ch = getchar();
  return ch1 == '-' ? -res : res;
}
inline char getch() {
  char ch = getchar();
  while (ch > 'z' || ch < 'a') ch = getchar();
  return ch;
}
void reset(bool t) {
  for (register int i = 0; i <= k; ++i)
    for (register int j = 0; j <= n; ++j) f[t][i][j] = -0x3f3f3f3f;
}
int main() {
  n = read();
  k = read();
  for (register int i = 1; i <= n; ++i) s[i] = getch();
  sa = getch();
  sb = getch();
  bool t = false;
  reset(t);
  f[t][0][0] = 0;
  for (register int i = 1; i <= n; ++i) {
    t ^= 1;
    reset(t);
    for (register int j = 0; j <= k; ++j) {
      for (register int a = 0; a <= n; ++a) {
        if (f[t ^ 1][j][a] < 0) continue;
        if (s[i] == sa) {
          if (sa == sb)
            f[t][j][a + 1] = max(f[t][j][a + 1], f[t ^ 1][j][a] + a);
          else
            f[t][j][a + 1] = max(f[t][j][a + 1], f[t ^ 1][j][a]);
        } else if (s[i] == sb)
          f[t][j][a] = max(f[t][j][a], f[t ^ 1][j][a] + a);
        else
          f[t][j][a] = max(f[t][j][a], f[t ^ 1][j][a]);
        if (j < k) {
          if (sa == sb)
            f[t][j + 1][a + 1] = max(f[t][j + 1][a + 1], f[t ^ 1][j][a] + a);
          else {
            f[t][j + 1][a + 1] = max(f[t][j + 1][a + 1], f[t ^ 1][j][a]);
            f[t][j + 1][a] = max(f[t][j + 1][a], f[t ^ 1][j][a] + a);
          }
        }
      }
    }
  }
  int ans = 0;
  for (register int i = 0; i <= k; ++i)
    for (register int j = 0; j <= n; ++j) ans = max(ans, f[t][i][j]);
  printf("%d\n", ans);
  return 0;
}
