#include <bits/stdc++.h>

using namespace std;

const int N = 1e6 + 5;
int n, m;
char ch[N];
int x[N], y[N];
int cnt[N], SA[N];
int rk[N], height[N];
inline void RadixSort() {
    for (register int i = 1; i <= m; ++i) {
        cnt[i] = 0;
    }
    for (register int i = 1; i <= n; ++i) {
        ++cnt[x[i]];
    }
    for (register int i = 1; i <= m; ++i) {
        cnt[i] += cnt[i - 1];
    }
    for (register int i = n; i >= 1; --i) {
        SA[cnt[x[y[i]]]--] = y[i], y[i] = 0;
    }
    return;
}

long long calc(string s) {
    n = s.size();
    m = 127;
    for (int i = 1; i <= n; ++i) ch[i] = s[i - 1];
    for (register int i = 1; i <= n; ++i) {
        x[i] = ch[i], y[i] = i;
    }
    RadixSort();
    for (register int p = 1; p < n; p <<= 1) {
        int tot = 0;
        for (register int i = n - p + 1; i <= n; ++i) {
            y[++tot] = i;
        }
        for (register int i = 1; i <= n; ++i) {
            if (SA[i] > p) {
                y[++tot] = SA[i] - p;
            }
        }
        RadixSort();
        swap(x, y);
        tot = x[SA[1]] = 1;
        for (register int i = 2; i <= n; ++i) {
            if (y[SA[i]] == y[SA[i - 1]] && y[SA[i] + p] == y[SA[i - 1] + p]) {
                x[SA[i]] = tot;
            } else {
                x[SA[i]] = (++tot);
            }
        }
        if (tot == n) {
            break;
        }
        m = tot;
    }
    for (register int i = 1; i <= n; ++i) {
        rk[SA[i]] = i;
    }
    for (register int i = 1; i <= n; ++i) {
        if (rk[i] == 1) {
            continue;
        }
        int k = height[rk[i - 1]];
        if (k) {
            --k;
        }
        int j = SA[rk[i] - 1];
        while (i + k <= n && j + k <= n && ch[i + k] == ch[j + k]) {
            ++k;
        }
        height[rk[i]] = k;
    }
    long long ans = 1ll * n * (n + 1) / 2;
    for (register int i = 1; i <= n; ++i) {
        ans -= height[i];
    }
    return ans;
}
signed main() {
    const int P = 998244353;
    int n, m; scanf("%d%d", &n, &m);
    string S; cin >> S;
    if (m == 1) printf("%lld\n", calc(S) % P);
    else {
        long long s1 = calc(S + S), s2 = calc(S + S + S);
        printf("%lld\n", (s1 % P + (s2 - s1) % P * ((m - 2) % P) % P) % P);
    }
    return 0;
}