#include <bits/stdc++.h>
using namespace std;
template <typename T>
void read(T &x) {
  x = 0;
  char ch = getchar();
  long long f = 1;
  while (!isdigit(ch)) {
    if (ch == '-') f *= -1;
    ch = getchar();
  }
  while (isdigit(ch)) {
    x = x * 10 + ch - 48;
    ch = getchar();
  }
  x *= f;
}
template <typename T, typename... Args>
void read(T &first, Args &...args) {
  read(first);
  read(args...);
}
template <typename T>
void write(T arg) {
  T x = arg;
  if (x < 0) {
    putchar('-');
    x = -x;
  }
  if (x > 9) {
    write(x / 10);
  }
  putchar(x % 10 + '0');
}
template <typename T, typename... Ts>
void write(T arg, Ts... args) {
  write(arg);
  if (sizeof...(args) != 0) {
    putchar(' ');
    write(args...);
  }
}
const long long mod = 1e9 + 7;
const int N = 250;
int n, k, f[N][N][N];
char s[N], t[N];
int main() {
  read(n, k);
  scanf("%s", s);
  scanf("%s", t);
  memset((f), -0x3f3f3f3f, sizeof(f));
  f[0][0][0] = 0;
  for (register int i = 0; i < n; ++i) {
    for (register int j = 0; j <= k; ++j) {
      for (register int l = 0; l <= n; ++l) {
        if (f[i][j][l] == -0x3f3f3f3f) {
          continue;
        }
        int e0 = s[i] == t[0];
        int e1 = s[i] == t[1];
        int e10 = t[0] == t[1];
        f[i + 1][j][l + e0] =
            max(f[i + 1][j][l + e0], f[i][j][l] + (e1 ? l : 0));
        if (j < k) {
          f[i + 1][j + 1][l + 1] =
              max(f[i + 1][j + 1][l + 1], f[i][j][l] + (e10 ? l : 0));
          f[i + 1][j + 1][l + e10] =
              max(f[i + 1][j + 1][l + e10], f[i][j][l] + l);
        }
      }
    }
  }
  int ans = 0;
  for (register int i = 0; i <= k; ++i) {
    for (register int j = 0; j <= n; ++j) {
      ans = max(ans, f[n][i][j]);
    }
  }
  write(ans), putchar('\n');
  return 0;
}
