#include <bits/stdc++.h>
using namespace std;
template <typename A, typename B>
string to_string(pair<A, B> p);
template <typename A, typename B, typename C>
string to_string(tuple<A, B, C> p);
template <typename A, typename B, typename C, typename D>
string to_string(tuple<A, B, C, D> p);
string to_string(const string &s) { return '"' + s + '"'; }
string to_string(const char *s) { return to_string((string)s); }
string to_string(bool b) { return (b ? "true" : "false"); }
string to_string(vector<bool> v) {
  bool first = true;
  string res = "{";
  for (int i = 0; i < static_cast<int>(v.size()); i++) {
    if (!first) {
      res += ", ";
    }
    first = false;
    res += to_string(v[i]);
  }
  res += "}";
  return res;
}
template <size_t N>
string to_string(bitset<N> v) {
  string res = "";
  for (size_t i = 0; i < N; i++) {
    res += static_cast<char>('0' + v[i]);
  }
  return res;
}
template <typename A>
string to_string(A v) {
  bool first = true;
  string res = "{";
  for (const auto &x : v) {
    if (!first) {
      res += ", ";
    }
    first = false;
    res += to_string(x);
  }
  res += "}";
  return res;
}
template <typename A, typename B>
string to_string(pair<A, B> p) {
  return "(" + to_string(p.first) + ", " + to_string(p.second) + ")";
}
template <typename A, typename B, typename C>
string to_string(tuple<A, B, C> p) {
  return "(" + to_string(get<0>(p)) + ", " + to_string(get<1>(p)) + ", " +
         to_string(get<2>(p)) + ")";
}
template <typename A, typename B, typename C, typename D>
string to_string(tuple<A, B, C, D> p) {
  return "(" + to_string(get<0>(p)) + ", " + to_string(get<1>(p)) + "," +
         to_string(get<2>(p)) + ", " + to_string(get<3>(p)) + ")";
}
void debug() { cerr << endl; }
template <typename Head, typename... Tail>
void debug(Head H, Tail... T) {
  cerr << " " << to_string(H);
  debug(T...);
}
struct Fast_power {
  long long integer(long long n, long long e,
                    long long my_mod = 9223372036854775807LL) {
    long long ans = 1;
    while (e) {
      if (e & 1)
        ans = (ans * n) % my_mod, e--;
      else
        n = (n * n) % my_mod, e >>= 1;
    }
    return ans;
  }
  vector<vector<long long>> matrix_multiply(vector<vector<long long>> a,
                                            vector<vector<long long>> b) {
    vector<vector<long long>> c(a.size(), vector<long long>(b[0].size(), 0));
    for (int i = 0; i < a.size(); i++)
      for (int q = 0; q < b[0].size(); q++) {
        long long num = 0;
        for (int e = 0; e < a[0].size(); i++) num += a[i][e] * b[e][q];
        c[i][q] = num;
      }
    return c;
  }
};
struct Euclidean {
  int gcdi(int a, int b) { return b ? gcdi(b, a % b) : a; }
  double gcdf(double a, double b, double accuracy) {
    return b <= accuracy ? a : gcdf(b, fmod(a, b), accuracy);
  }
};
const int maxnD = 100000 + 5;
const long long INFD = 0x3f3f3f3f;
;
struct Dijkstra {
  struct Edge {
    int from, to;
    long long dist;
  };
  struct HeapNode {
    long long d;
    int u;
    bool operator<(const HeapNode &rhs) const { return d > rhs.d; }
  };
  vector<Edge> edges;
  vector<int> G[maxnD];
  bool done[maxnD];
  long long d[maxnD];
  int p[maxnD], n;
  void init(int n) {
    this->n = n;
    for (int i = 0; i <= n; i++) G[i].clear();
    edges.clear();
  }
  void AddEdge(int from, int to, long long dist) {
    edges.push_back((Edge){from, to, dist});
    int m = edges.size();
    G[from].push_back(m - 1);
  }
  void dijkstra(int s) {
    priority_queue<HeapNode> q;
    memset(d, INFD, sizeof(d));
    d[s] = 0;
    memset(done, 0, sizeof(done));
    q.push((HeapNode){0, s});
    while (!q.empty()) {
      HeapNode x = q.top();
      q.pop();
      int u = x.u;
      if (done[u]) continue;
      done[u] = true;
      for (int i = 0; i < G[u].size(); i++) {
        Edge &e = edges[G[u][i]];
        if (d[e.to] > d[u] + e.dist) {
          d[e.to] = d[u] + e.dist;
          p[e.to] = G[u][i];
          q.push((HeapNode){d[e.to], e.to});
        }
      }
    }
  }
};
const int maxnL = 500000 + 5;
const int INFL = 0x3f3f3f3f;
struct LIS {
  int g[maxnL], a[maxnL], d[maxnL];
  void lis(int n) {
    for (int i = 1; i <= n; i++) g[i] = INFL;
    for (int i = 1; i < n; i++) {
      int k = lower_bound(g + 1, g + n + 1, a[i]) - g;
      g[k] = a[i];
    }
  }
};
const int maxnS = 200000 + 5;
struct SegmentTree {
  int a[maxnS];
  int sumv[maxnS * 4], minv[maxnS * 4], maxv[maxnS * 4], addv[maxnS * 4],
      setv[maxnS * 4];
  int lc, rc, v;
  int _min, _max, _sum;
  void build(int l, int r, int o) {
    if (l == r) return void(sumv[o] = minv[o] = maxv[o] = a[l]);
    build(l, (l + r) >> 1, o << 1);
    build(((l + r) >> 1) + 1, r, o << 1 | 1);
  }
  void maintain(int l, int r, int o) {
    sumv[o] = minv[o] = maxv[o] = a[l];
    if (r > l) {
      sumv[o] = sumv[o << 1] + sumv[o << 1 | 1];
      minv[o] = min(minv[o << 1], minv[o << 1 | 1]);
      maxv[o] = max(maxv[o << 1], maxv[o << 1 | 1]);
    }
    minv[o] += addv[o], maxv[o] += addv[o], sumv[o] += addv[o] * (r - l + 1);
  }
  void update(int l, int r, int o) {
    if (l >= lc && r <= rc)
      addv[o] += v;
    else {
      int m = (l + r) >> 1;
      if (lc <= m) update(l, (l + r) >> 1, o << 1);
      if (rc > m) update(((l + r) >> 1) + 1, r, o << 1 | 1);
    }
    maintain(l, r, o);
  }
  void query(int l, int r, int o, int add) {
    if (lc <= l && r <= rc) {
      _sum += sumv[o] + add * (r - l + 1);
      _min = min(_min, minv[o] + add);
      _max = max(_max, maxv[o] + add);
    } else {
      int m = (l + r) >> 1;
      if (lc <= m) query(l, m, o << 1, add + addv[o]);
      if (rc > m) query(m + 1, r, o << 1 | 1, add + addv[o]);
    }
  }
};
const int maxnB = 100000 + 5;
struct BIT {
  int c[maxnB], n;
  int lowbit(int x) { return x & -x; }
  int sum(int x) {
    int ret = 0;
    while (x > 0) {
      ret += c[x];
      x -= lowbit(x);
    }
    return ret;
  }
  void add(int x, int d) {
    while (x <= n) {
      c[x] += d;
      x += lowbit(x);
    }
  }
};
const int INF = 0x3f3f3f3f;
const int maxn = 200 + 5;
int d[maxn][maxn][maxn], f[maxn][maxn][maxn];
char str[maxn], s[maxn];
signed main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  int n, k;
  cin >> n >> k;
  memset(d, -1, sizeof(d));
  d[0][0][0] = 0;
  cin >> str + 1 >> s;
  for (int i = 1; i <= n; i++)
    for (int q = 0; q <= k; q++)
      for (int e = 0; e <= n; e++) {
        if (d[i - 1][q][e] != -1) d[i][q][e] = d[i - 1][q][e];
        if (str[i] == s[1])
          if (d[i - 1][q][e] != -1)
            d[i][q][e] = max(d[i][q][e], d[i - 1][q][e] + e);
        if (e > 0 && str[i] == s[0])
          if (d[i - 1][q][e - 1] != -1)
            d[i][q][e] = max(d[i - 1][q][e - 1], d[i][q][e]);
        if (q > 0) {
          if (d[i - 1][q - 1][e] != -1)
            d[i][q][e] = max(d[i][q][e], d[i - 1][q - 1][e] + e);
          if (e > 0 && d[i - 1][q - 1][e - 1] != -1)
            d[i][q][e] = max(d[i - 1][q - 1][e - 1], d[i][q][e]);
        }
      }
  int ans = 0;
  for (int i = 1; i <= n; i++)
    for (int q = 0; q <= k; q++)
      for (int e = 0; e <= n; e++) ans = max(d[i][q][e], ans);
  if (s[0] == s[1]) {
    int num = 0;
    for (int i = 1; i <= n; i++)
      if (str[i] == s[0]) num++;
    int num2 = num + min(k, n - num);
    ans = num2 * (num2 - 1) / 2;
  }
  cout << ans << endl;
  return 0;
}
