#include <algorithm>
#include <cstdio>
#include <cstring>
#include <iostream>

using namespace std;

const int N = 900000+100;
typedef long long ll;
ll mod = 998244353;
int m, p, rk[N * 2], oldrk[N], sa[N * 2], oldsa[N], cnt[N], height[N];
ll good(string &temp) {
    //string s = temp;
    //int n = s.length() - 1;
    string s = temp;
    int n = s.length() - 1;
    fill(rk, rk + 1 + n+n, 0);
    fill(oldrk, oldrk + 1 + n, 0);
    fill(sa, sa + 1 + n+n, 0);
    fill(oldsa, oldsa + 1 + n, 0);
    fill(cnt, cnt + 1 + n, 0);
    fill(height, height + 1 + n, 0);
    for (int i = 1; i <= n; i++) {
        sa[i] = i; rk[i] = s[i];
    }
    for (int w = 1; w < n; w <<= 1) {
        auto cp = [w](int &x, int &y) {
            return (rk[x] == rk[y] ? rk[x + w] < rk[y + w] : rk[x] < rk[y]);
            };
        sort(sa + 1, sa + 1 + n, cp);
        memcpy(oldrk, rk, (n + 1) * sizeof(int));
        int p = 0;
        for (int i = 1; i <= n; i++) {
            if (oldrk[sa[i]] == oldrk[sa[i - 1]] && oldrk[sa[i] + w] == oldrk[sa[i - 1] + w]) {
                rk[sa[i]] = p;
            }
            else {
                rk[sa[i]] = ++p;
            }
        }
    }
    int i,k;
    for (i = 1, k = 0; i <= n; ++i) {
        if (rk[i] == 0) continue;
        if (k) --k;
        while (s[i + k] == s[sa[rk[i] - 1] + k]) ++k;
        height[rk[i]] = k;
    }
    long long ans = 1ll * n * (n + 1) / 2;
    for (int i = 1; i <= n; i++) {
            ans -= height[i];
    }
    return ans%mod;
}
int main() {
    int n, m;
    cin >> n >> m;
    string tar;
    cin >> tar;
    if (m <= 2) {
        string temp = "@";
        for (int i = 1; i <= m; i++) {
            temp += tar;
        }
        cout << good(temp);
    }
    else {
        string temp = "@"+tar+tar;
        ll ok = good(temp);
        temp += tar;
        ll d = (good(temp) - ok + mod) % mod;
        ll ext = (m - 2) % mod * d % mod;
        ok = (ok + ext) % mod;
        cout << ok;
    }
    return 0;
}