#include<bits/stdc++.h>
using namespace std;

#define int long long
#define REP(i,m,n) for(int i=(m);i<(n);i++)
#define rep(i,n) REP(i,0,n)
#define pb push_back
#define all(a) a.begin(),a.end()
#define rall(c) (c).rbegin(),(c).rend()
#define mp make_pair
#define endl '\n'
//#define vec vector<ll>
//#define mat vector<vector<ll> >
#define fi first
#define se second
#define double long double
typedef long long ll;
typedef unsigned long long ull;
typedef pair<ll,ll> pll;
//typedef long double ld;
typedef complex<double> Complex;
const ll INF=1e9+7;
const ll MOD=998244353;
const ll inf=INF*INF;
const ll mod=MOD;
const ll MAX=100010;
const double PI=acos(-1.0);
typedef vector<vector<ll> > mat;
typedef vector<ll> vec;

//二分累乗

ll rui(ll a,ll b){
    ll res=1;
    ll x=a;
    while(b){
        if(b&1)res=res*x%mod;
        x=x*x%mod;
        b/=2;
    }
    return res;
}

void solve(){
    ll n;cin>>n;
    string s;cin>>s;
    ll cnt=0;
    ll ans=0;
    rep(i,n){
        if(s[i]=='a'){
            cnt++;
            continue;
        }
        ll pl=s[i]-'b';
        if(cnt==0){
            if(i<n-1){
                ans+=rui(25,n-i-2)*(n-i-1)%mod*pl%mod;
                ans%=mod;
            }
            ans+=rui(25,n-i-1);
            ans%=mod;
        }else if(cnt==1){
            ans+=rui(25,n-i-1)*pl;
            ans%=mod;
        }
    }
    cout<<ans<<endl;
}

signed main(){
    //cin.tie(0);
    //ios::sync_with_stdio(false);
    solve();
}