#include <bits/stdc++.h>
using namespace std;
using ll = long long;
const ll MOD = 998244353;
using P = pair<int,int>;
#define rep(i, n) for(int i = 0; i < n; i++)
#define all(x) (x).begin(),(x).end()
ll mpow(ll x, ll y){
    ll res = 1; x %= MOD;
    while(y){
        if(y%2) res = res * x % MOD;
        x = x * x % MOD;
        y /= 2;
    }
    return res;
}
int main(){
    int n;
    string s;
    cin >> n >> s;
    bool seena = false;
    ll ans = 0;
    rep(i,n){
        int x = s[i] - 'a';
        if(!x){
            if(seena) break;
            else{
                seena = true;
                continue;
            }
        }
        if(!seena) ans = (ans + (mpow(25,n-i-1) + mpow(25,n-i-2)*(x-1)*(n-i-1))) % MOD;
        else ans = (ans + mpow(25,n-i-1) * (x-1)) % MOD;
    }
    cout << ans << endl;
    return 0;
}