#include <bits/stdc++.h>
using i64 = long long;
#define int i64
#define pb push_back
#define ep emplace
#define eb emplace_back
using std::cerr;
using std::max, std::min, std::swap, std::array;
using std::cin, std::cout, std::string, std::vector;
int read(int x = 0, int f = 0, char ch = getchar()) {
    while (ch < 48 or 57 < ch) f = ch == 45, ch = getchar();
    while(48 <= ch and ch <= 57) x = x * 10 + ch - 48, ch = getchar();
    return f ? -x : x;
}
using std::ostream;
template <class T1, class T2> ostream &operator<<(ostream &os, const std::pair<T1, T2> &a) { return os << "(" << a.first << ", " << a.second << ")"; };
template <class T> ostream &operator<<(ostream &os, const vector<T> &as) { const int sz = as.size(); os << "["; for (int i = 0; i < sz; ++i) { if (i >= 256) { os << ", ..."; break; } if (i > 0) { os << ", "; } os << as[i]; } return os << "]"; }
template <class T> void pv(T a, T b) { for (T i = a; i != b; ++i) cerr << *i << " "; cerr << '\n'; }
using pii = std::pair<int, int>;
#define fi first
#define se second
template <class T>
constexpr T power(T a, i64 b) { T res {1}; for (; b; b /= 2, a *= a) if (b % 2) res *= a; return res; }
constexpr i64 mul(i64 a, i64 b, i64 p) { i64 res = a * b - (i64)(1.L * a * b / p) * p; res %= p; if (res < 0) res += p; return res; }
template <i64 P>
struct MInt {
    i64 x;
    constexpr MInt() : x {0} {}
    constexpr MInt(i64 x) : x {norm(x % getMod())} {}
    static i64 Mod;
    constexpr static i64 getMod() { return P > 0 ? P : Mod; }
    constexpr static void setMod(i64 Mod_) { Mod = Mod_; }
    constexpr i64 norm(i64 x) const { if (x < 0) x += getMod(); if (x >= getMod()) x -= getMod(); return x; }
    constexpr i64 val() const { return x; }
    constexpr MInt operator-() const { MInt res; res.x = norm(getMod() - x); return res; }
    constexpr MInt inv() const { return power(*this, getMod() - 2); }
    constexpr MInt &operator*=(MInt rhs) & { if (getMod() < (1ULL << 31)) x = x * rhs.x % int(getMod()); else x = mul(x, rhs.x, getMod()); return *this; }
    constexpr MInt &operator+=(MInt rhs) & { x = norm(x + rhs.x); return *this; }
    constexpr MInt &operator-=(MInt rhs) & { x = norm(x - rhs.x); return *this; }
    constexpr MInt &operator/=(MInt rhs) & { return *this *= rhs.inv(); }
    friend constexpr MInt operator*(MInt lhs, MInt rhs) { MInt res = lhs; res *= rhs; return res; }
    friend constexpr MInt operator+(MInt lhs, MInt rhs) { MInt res = lhs; res += rhs; return res; }
    friend constexpr MInt operator-(MInt lhs, MInt rhs) { MInt res = lhs; res -= rhs; return res; }
    friend constexpr MInt operator/(MInt lhs, MInt rhs) { MInt res = lhs; res /= rhs; return res; }
    friend constexpr std::istream &operator>>(std::istream &is, MInt &a) { i64 v; is >> v; a = MInt(v); return is; }
    friend constexpr std::ostream &operator<<(std::ostream &os, const MInt &a) { return os << a.val(); }
    friend constexpr bool operator==(MInt lhs, MInt rhs) { return lhs.val() == rhs.val(); }
    friend constexpr bool operator!=(MInt lhs, MInt rhs) { return lhs.val() != rhs.val(); }
    friend constexpr bool operator<(MInt lhs, MInt rhs) { return lhs.val() < rhs.val(); }
};
template <>
i64 MInt<0>::Mod = 998244353;
constexpr int P = 998244353;
using Z = MInt<P>;

struct SAM {
    static constexpr int ALPHABET_SIZE = 26;
    struct Node {
        int len;
        int link;
        std::array<int, ALPHABET_SIZE> next;
        Node() : len{}, link{}, next{} {}
    };
    std::vector<Node> t;
    SAM() {
        init();
    }
    void init() {
        t.assign(2, Node());
        t[0].next.fill(1);
        t[0].len = -1;
    }
    int newNode() {
        t.emplace_back();
        return t.size() - 1;
    }
    int extend(int p, int c) {
        if (t[p].next[c]) {
            int q = t[p].next[c];
            if (t[q].len == t[p].len + 1) {
                return q;
            }
            int r = newNode();
            t[r].len = t[p].len + 1;
            t[r].link = t[q].link;
            t[r].next = t[q].next;
            t[q].link = r;
            while (t[p].next[c] == q) {
                t[p].next[c] = r;
                p = t[p].link;
            }
            return r;
        }
        int cur = newNode();
        t[cur].len = t[p].len + 1;
        while (!t[p].next[c]) {
            t[p].next[c] = cur;
            p = t[p].link;
        }
        t[cur].link = extend(p, c);
        return cur;
    }
    
    int next(int p, int x) {
        return t[p].next[x];
    }
     
    int link(int p) {
        return t[p].link;
    }
    
    int len(int p) {
        return t[p].len;
    }
    
    int size() {
        return t.size();
    }
};

const int inf = 1e18;

void solve() {
    int n = read();
    int m = read();

    SAM sam;

    string s;
    cin >> s;

    int p = 1;
    for (auto c : s) {
        p = sam.extend(p, c - 'a');
    }
    for (auto c : s) {
        p = sam.extend(p, c - 'a');
    }


    Z ans1 = 0;
    for (int i = 2; i < sam.size(); i++) {
        ans1 += sam.len(i) - sam.len(sam.link(i));
    }

    for (auto c : s) {
        p = sam.extend(p, c - 'a');
    }
    Z ans2 = 0;
    for (int i = 2; i < sam.size(); i++) {
        ans2 += sam.len(i) - sam.len(sam.link(i));
    }

    Z ans = (ans2 - ans1) * Z(m - 2LL) + ans1;

    cout << ans << '\n';
}

signed main() {
    // for (int T = read(); T--; solve());
    solve();
    return 0;
}