#include <bits/stdc++.h>

#define rep(i, j, k) for (int i = (j); i <= (k); ++i)
#define per(i, j, k) for (int i = (j); i >= (k); --i)
#define SZ(v) int((v).size())
#define ALL(v) (v).begin(),(v).end()
#define fi first
#define se second
using ll = long long;
using pii = std::pair<int, int>;
using pll = std::pair<ll, ll>;

template<class T>inline void chkmn(T &x, T y) { if (y < x) x = y; }
template<class T>inline void chkmx(T &x, T y) { if (y > x) x = y; }

using namespace std;

template <int P>
class mod_int {
  using Z = mod_int;

private:
  static int mo(int x) { return x < 0 ? x + P : x; }

public:
  int x;
  int val() const { return x; }
  mod_int() : x(0) {}
  template <class T>
  mod_int(const T &x_) : x(x_ >= 0 && x_ < P ? static_cast<int>(x_) : mo(static_cast<int>(x_ % P))) {}
  bool operator==(const Z &rhs) const { return x == rhs.x; }
  bool operator!=(const Z &rhs) const { return x != rhs.x; }
  Z operator-() const { return Z(x ? P - x : 0); }
  Z pow(long long k) const {
    Z res = 1, t = *this;
    while (k) {
      if (k & 1) res *= t;
      if (k >>= 1) t *= t;
    }
    return res;
  }
  Z &operator++() {
    x < P - 1 ? ++x : x = 0;
    return *this;
  }
  Z &operator--() {
    x ? --x : x = P - 1;
    return *this;
  }
  Z operator++(int) {
    Z ret = x;
    x < P - 1 ? ++x : x = 0;
    return ret;
  }
  Z operator--(int) {
    Z ret = x;
    x ? --x : x = P - 1;
    return ret;
  }
  Z inv() const { return pow(P - 2); }
  Z &operator+=(const Z &rhs) {
    (x += rhs.x) >= P && (x -= P);
    return *this;
  }
  Z &operator-=(const Z &rhs) {
    (x -= rhs.x) < 0 && (x += P);
    return *this;
  }
  Z &operator*=(const Z &rhs) {
    x = 1ULL * x * rhs.x % P;
    return *this;
  }
  Z &operator/=(const Z &rhs) { return *this *= rhs.inv(); }
#define setO(T, o)                                 \
  friend T operator o(const Z &lhs, const Z &rhs) {\
    Z res = lhs;                                   \
    return res o## = rhs;                          \
  }
  setO(Z, +) setO(Z, -) setO(Z, *) setO(Z, /)
#undef setO
};
const int P = 998244353;
using Z = mod_int<P>;

const int maxn = 1000010;

namespace SA {
  // init: len = m, |char| = sigma, string = a[]
  int m, sigma, a[maxn], rnk[maxn], sa[maxn], h[maxn], cnt[maxn], p[maxn];
  
  void SA_sort() {
    rep (i, 1, sigma) cnt[i] = 0;
    rep (i, 1, m) cnt[rnk[i]] += 1;
    rep (i, 1, sigma) cnt[i] += cnt[i - 1];
    per (i, m, 1) sa[cnt[rnk[p[i]]]--] = p[i];
  }
  
  void Get_SA() {
    rep (i, 1, m) rnk[i] = a[i], p[i] = i;
    SA_sort();
    for (int len = 1, tot = 0; tot < m; sigma = tot, len <<= 1) {
      tot = 0;
      per (i, m, m - len + 1) p[++tot] = i;
      rep (i, 1, m) if (sa[i] > len) p[++tot] = sa[i] - len;
      SA_sort();
      rep (i, 1, m) p[i] = rnk[i];
      rnk[sa[1]] = tot = 1;
      rep (i, 2, m) {
        if (p[sa[i - 1]] == p[sa[i]] &&
          p[sa[i - 1] + len] == p[sa[i] + len]) rnk[sa[i]] = tot;
        else rnk[sa[i]] = ++tot;
      }
    }
    rep (i, 1, m) rnk[sa[i]] = i;
  }
  
  void Get_Height() {
    int k = 0;
    rep (i, 1, m) {
      if (rnk[i] == 1) continue;
      k = max(k - 1, 0);
      int j = sa[rnk[i] - 1];
      while (max(i, j) + k <= m && a[i + k] == a[j + k]) k++;
      h[rnk[i]] = k;
    }
  }
}

ll calc(string s) {
  int n = s.length();
  SA::m = n, SA::sigma = 26;
  rep (i, 1, n) SA::a[i] = s[i - 1] - 'a' + 1;
  SA::Get_SA(), SA::Get_Height();
  ll ans = 1ll * n * (n + 1) / 2;
  rep (i, 1, n) ans -= SA::h[i];
  return ans;
}

int n, m;
string s;

int main() {
  cin.tie(nullptr) -> ios::sync_with_stdio(false);
  cin >> n >> m >> s;
  Z a = calc(s), b = calc(s + s), c = calc(s + s + s);
  if (m == 1) cout << a.val() << '\n';
  else if (m == 2) cout << b.val() << '\n';
  else cout << (b + (c - b) * (m - 2)).val() << '\n';
}