#include<bits/stdc++.h>
const int N = 3e5+5, base = 233, mod = 998244353;
using u64 = unsigned long long;
using L = __uint128_t;
struct FastMod {
    u64 b, m;
    FastMod(u64 b): b(b), m(u64((L(1) << 64) / b)) {}
    u64 reduce(u64 a) {
        u64 q = (u64)((L(m) * a) >> 64);
        u64 r = a - q * b; 
        return r >= b ? r - b: r ;
    }
} F(mod);
int n, m, len, hash[N * 3], pw[N * 3], rk[N * 3]; char s[N * 3];
inline int ask(int l, int r) {
    return F.reduce(hash[r] - F.reduce(1ll * hash[l - 1] * pw[r - l + 1]) + mod);
}
bool cmp(int a, int b) {
    if(a > b) return !cmp(b, a);
    if(a == b) return false;
    if(s[a] != s[b]) return s[a] < s[b];
    int l = 1, r = std::min(len - a + 1, len - b + 1);
    while(l < r) {
        int mid = (l + r) >> 1;
        if(ask(a, a + mid - 1) ^ ask(b, b + mid - 1)) r = mid;
        else l = mid + 1;
    }
    if(ask(a, a + l - 1) == ask(b, b + l - 1)) return true;
    else return s[a + l - 1] < s[b + l - 1];
}
int lcp(int a, int b) {
    if(a > b) return lcp(b, a);
    if(s[a] != s[b]) return 0;
    int l = 1, r = std::min(len - a + 1, len - b + 1);
    while(l < r) {
        int mid = (l + r) >> 1;
        if(ask(a, a + mid - 1) ^ ask(b, b + mid - 1)) r = mid;
        else l = mid + 1;
    }
    if(ask(a, a + l - 1) ^ ask(b, b + l - 1)) --l;
    return l;
}
int solve() {
    hash[1] = s[1] - 'a';
    for(int i = 2; i <= len; ++i) hash[i] = F.reduce(1ll * hash[i - 1] * base + (s[i] - 'a'));
    for(int i = 1; i <= len; ++i) rk[i] = i;
    std::sort(rk + 1, rk + len + 1, cmp);
    int ans = 1ll * len * (len + 1) / 2 % mod;
    //for(int i = 1; i <= n; ++i) printf("%d ", rk[i]); puts("");
    for(int i = 1; i < len; ++i) ans = F.reduce(ans + mod - lcp(rk[i], rk[i + 1]));
    return ans;
}
signed main() {
    scanf("%d%d%s", &n, &m, s + 1), pw[0] = 1;
    for(int i = 1; i <= n * 3; ++i) pw[i] = F.reduce(1ll * pw[i - 1] * base);
    for(int i = 1; i <= n; ++i) s[i + n] = s[i + 2 * n] = s[i];
    if(m <= 3) {
        len = n * m;
        printf("%d\n", solve());
        return 0;
    }
    int res2, res3;
    len = 3 * n, res3 = solve();
    len = 2 * n, res2 = solve();
    // printf("%d %d\n", res2, res3);
    printf("%lld\n", (res2 + 1ll * (res3 - res2 + mod) % mod * (m - 2) % mod) % mod);
    return 0;
}