#include<bits/stdc++.h>
const int N = 3e5+5, base = 233, mod = 998244353;
using i64 = long long;
using u64 = unsigned long long;
int n, m, len, rk[N * 3]; char s[N * 3];
u64 hash[N * 3], pw[N * 3];
#define max(a,b) ((a) > (b)? (a): (b))
#define min(a,b) ((a) < (b)? (a): (b))
inline u64 ask(int l, int r) {
    return hash[r] - hash[l - 1] * pw[r - l + 1];
}
bool cmp(int a, int b) {
    if(s[a] != s[b]) return s[a] < s[b];
    int l = 1, r = 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 a > b;
    else return s[a + l - 1] < s[b + l - 1];
}
inline int lcp(int a, int b) {
    if(s[a] != s[b]) return 0;
    int l = 1, r = 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;
}
inline i64 solve() {
    for(int i = 1; i <= len; ++i) rk[i] = i;
    std::stable_sort(rk + 1, rk + len + 1, cmp);
    i64 ans = 1ll * len * (len + 1) / 2;
    //for(int i = 1; i <= n; ++i) printf("%d ", rk[i]); puts("");
    for(int i = 1; i < len; ++i) ans -= 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] = pw[i - 1] * base;
    for(int i = 1; i <= n; ++i) s[i + n] = s[i + 2 * n] = s[i];
    for(int i = 1; i <= n * 3; ++i) hash[i] = hash[i - 1] * base + (s[i] - 'a');
    if(m <= 3) {
        len = n * m;
        printf("%lld\n", solve() % mod);
        return 0;
    }
    int res2, res3;
    len = 3 * n, res3 = solve() % mod;
    len = 2 * n, res2 = solve() % mod;
    printf("%lld\n", (res2 + 1ll * (res3 - res2 + mod) % mod * (m - 2) % mod) % mod);
    return 0;
}