#include <bits/stdc++.h>
using namespace std;

#define ll long long

const int N = 900005;
const int mod = 998244353;

struct SAM {
    int ch[3 * N][26], fail[3 * N], len[3 * N];
    int tot, lst;
    SAM() { 
        memset(ch, 0, sizeof(ch));
        memset(fail, 0, sizeof(fail));
        memset(len, 0, sizeof(len));
        lst = tot = 1; 
    }
    void extend(int x) {
        int u = lst; lst = ++tot;
        len[lst] = len[u] + 1;
        for (; ch[u][x] == 0; u = fail[u]) ch[u][x] = lst;
        if (!u) {
            fail[lst] = 1;
            return;
        }
        int v = ch[u][x];
        if (len[v] == len[u] + 1) {
            fail[lst] = v;
            return;
        }
        int w = ++tot;
        len[w] = len[u] + 1, fail[w] = fail[v];
        memcpy(ch[w], ch[v], sizeof(ch[v]));
        fail[v] = fail[lst] = w;
        for (; ch[u][x] == v; u = fail[u]) ch[u][x] = w;
    }
    ll calc() {
        ll ans = 0;
        for (int i = 2; i <= tot; i++)
            ans += len[i] - len[fail[i]];
        return ans;
    }
};

ll calc(string s) {
    SAM sam;
    for (auto it: s) sam.extend(it - 'a');
    return sam.calc();
}

int main() {
    ios::sync_with_stdio(false), cin.tie(0);
    int n, m;
    string s;
    cin >> n >> m;
    cin >> s;
    if (m == 1) {
        cout << calc(s) % mod << '\n';
    } else {
        ll coef1 = calc(s + s), coef2 = calc(s + s + s);
        // printf("coef1 = %lld, coef2 = %lld\n", coef1, coef2);
        cout << (coef1 + (coef2 - coef1) % mod * (m - 2)) % mod;
    }
    return 0;
}