#include <bits/stdc++.h>
int ***sol;
int N, K;
const int kInvalidSol = -10000;
void new_sol() {
  sol = (int ***)malloc(sizeof(int **) * (N + 1));
  for (int n = 0; n <= N; ++n) {
    sol[n] = (int **)malloc(sizeof(int *) * (K + 1));
    for (int k = 0; k <= K; ++k) {
      sol[n][k] = (int *)malloc(sizeof(int) * (N + 1));
      for (int i = 0; i <= N; ++i) {
        sol[n][k][i] = kInvalidSol;
      }
    }
  }
}
void free_sol() {
  for (int i = 0; i <= N; ++i) {
    for (int j = 0; j <= K; ++j) {
      free(sol[i][j]);
    }
    free(sol[i]);
  }
  free(sol);
}
void try_update_sol(int n, int k, int i, int value) {
  if (value >= 0 && sol[n][k][i] < value) {
    sol[n][k][i] = value;
  }
}
int imax(int a, int b) { return a < b ? b : a; }
int main() {
  char s[201], t[3];
  scanf("%d%d\n%s\n%s", &N, &K, s, t);
  new_sol();
  if (t[0] == t[1]) {
    int cc = 0;
    for (int i = 0; i < N; ++i) {
      if (s[i] == t[0]) {
        ++cc;
      }
    }
    cc += K;
    if (cc > N) {
      cc = N;
    }
    printf("%d\n", cc * (cc - 1) / 2);
  } else {
    {
      int cc = 0;
      sol[0][0][0] = 0;
      for (int n = 1; n <= N; ++n) {
        if (s[n - 1] == t[0]) {
          ++cc;
          if (cc == 1) {
            sol[n][0][1] = 0;
          } else {
            try_update_sol(n, 0, cc, sol[n - 1][0][cc - 1]);
          }
        } else if (s[n - 1] == t[1]) {
          try_update_sol(n, 0, cc, sol[n - 1][0][cc] + cc);
        } else {
          try_update_sol(n, 0, cc, sol[n - 1][0][cc]);
        }
        for (int k = cc; k <= K; ++k) {
          try_update_sol(n, k, 0, 0);
        }
      }
    }
    for (int k = 1; k <= K; ++k) {
      try_update_sol(1, k, 1, 0);
      for (int n = 2; n <= N; ++n) {
        for (int i = 1; i <= n; ++i) {
          try_update_sol(n, k, i, sol[n][k - 1][i]);
          if (s[n - 1] == t[0]) {
            try_update_sol(n, k, i, sol[n - 1][k][i - 1]);
            try_update_sol(n, k, i, sol[n - 1][k - 1][i] + i);
          } else if (s[n - 1] == t[1]) {
            try_update_sol(n, k, i, sol[n - 1][k][i] + i);
            try_update_sol(n, k, i, sol[n - 1][k - 1][i - 1]);
          } else {
            try_update_sol(n, k, i, sol[n - 1][k - 1][i - 1]);
            try_update_sol(n, k, i, sol[n - 1][k - 1][i] + i);
            try_update_sol(n, k, i, sol[n - 1][k][i]);
          }
        }
      }
    }
    int max = 0;
    for (int i = 1; i <= N; ++i) {
      if (sol[N][K][i] > max) {
        max = sol[N][K][i];
      }
    }
    printf("%d\n", max);
    free_sol();
  }
  return 0;
}
