#include<bits/stdc++.h>
namespace rgs = std::ranges;
using std::cin, std::cout;
using ll = long long;
using u64 = unsigned long long;
using db = double;
const int N = 300005 * 2 * 2;
const int mod = 998244353;
int c[N][26], mx[N], fail[N], tot = 1;
int append(int id, int w) {
	int p = id, now = ++tot;
	for(mx[now] = mx[p] + 1;p && !c[p][w];p = fail[p])
		c[p][w] = now;
	if(!p) fail[now] = 1;
	else {
		int q = c[p][w];
		if(mx[q] == mx[p] + 1) fail[now] = q;
		else {
			int x = ++tot; mx[x] = mx[p] + 1;
			memcpy(c[x], c[q], sizeof(c[0])), fail[x] = fail[q];
			for(fail[q] = fail[now] = x;p && c[p][w] == q;p = fail[p])
				c[p][w] = x;
		}
	}
	return now;
}
std::vector<int> e[N];
int vis[N];

std::vector<std::pair<int, int>> seq;
int n, m;
char s[N];

void dfs0(int x) {
	if(vis[x]) seq.emplace_back(x, vis[x]);
	for(int y : e[x]) {
		dfs0(y);
	}
}
int lca(int x, int y) {
	for(;x != y;) {
		if(mx[x] > mx[y]) std::swap(x, y);
		y = fail[y];
	}
	return x;
}
int main() {
	std::ios::sync_with_stdio(false), cin.tie(0);
	cin >> n >> m;
	for(int i = 1;i <= n;++i) {
		cin >> s[i];
		s[i + n] = s[i];
	}
	const int p = n * std::min(m, 2);
	std::vector<int> id(p + 1);
	int x = 1;
	for(int i = 1;i <= p;++i) {
		id[i] = x = append(x, s[i] - 'a');
	}
	for(int i = 2;i <= tot;++i) e[fail[i]].push_back(i);
	for(int i = 1;i <= n;++i) {
		const int j = i + (m == 1 ? 0 : n);
		vis[id[j]] = j;
	}
	dfs0(1);
	ll ans = 0;
	for(int i = 1;i <= n;++i) {
		ans += i;
		ans += ll(m - 1) * n;
		ans %= mod;
	}
	for(int i = 1;i < n;++i) {
		auto [sx, x] = seq[i - 1];
		auto [sy, y] = seq[i];
		ll lcp = mx[lca(sx,  sy)];
		if(lcp >= n) lcp = std::min(x, y) + (ll) n * (m - 2);
		ans -= lcp;
		ans %= mod;
	}
	cout << (ans + mod) % mod << '\n';
}