#include <bits/stdc++.h>
#include <atcoder/all>
#include <boost/polygon/point_data.hpp>
#include <boost/polygon/voronoi.hpp>
#define rep(i,a,b) for(int i=(a);i<(b);i++)
#define rrep(i,a,b) for(int i=(b)-1;i>=(a);i--)
#define all(x) begin(x),end(x)
#define sz(x) (int)(x).size()
using namespace std;
using namespace atcoder;
using ll=long long;
using ld=long double;
using vll=vector<ll>;
using vvll=vector<vll>;
using vi=vector<int>;
using vvi=vector<vi>;
using pll=pair<ll,ll>;
using pi=pair<int,int>;

using mint=modint998244353;

// using BoostPoint=boost::polygon::point_data<int>;
// using Voronoi=boost::polygon::voronoi_diagram<double>;

int main()
{
  	ios::sync_with_stdio(false);
	cin.tie(nullptr);

	int N;
	string S;
	cin>>N>>S;
	mint ans=0;
	int p=0;
	rep(i,0,N){
		int t=S[i]-'a';
		int m=N-i-1;
		mint f0=mint(25).pow(m);
		mint f1=0;
		if(m>0)f1=m*mint(25).pow(m-1);
		if(p==0){
			if(t>0)ans+=f0+(t-1)*f1;
		}else if(p==1){
			if(t>0)ans+=(t-1)*f0;
		}else{
			break;
		}
		if(S[i]=='a')p++;
	}
	cout<<ans.val()<<'\n';

}