#include <bits/stdc++.h>
const int mod = 998244353;
using namespace std;
int n, m, p, k, q;
int dp[5010];
char s[5010];
int ksm(int a, int k) {
    int ans = 1;

    for (; k; k >>= 1, a = 1ll * a * a % mod)
        if (k & 1)
            ans = 1ll * ans * a % mod;

    return ans;
}
int main() {
    scanf("%d%s", &m, s + 1);
    n = strlen(s + 1);
    n = min(n, m);
    int i, j;

    for (i = 1, j = 2; j <= n && s[i] <= s[j]; j++)
        s[i] < s[j] ? i = 1 : i++;

    n = j - i, s[n]--;
    dp[0] = 1;

    for (i = 1; i <= m; i++) {
        for (j = 1; j <= min(i, n); j++) {
            dp[i] = (dp[i] + 1ll * ('z' - s[j]) * dp[i - j] % mod * (i < m ? 1 : j)) % mod;
        }
    }

    printf("%d\n", (ksm(26, m) - dp[m] + mod) % mod);
}