#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
typedef long long int ll;
typedef long double ld;
#define FOR(i,l,r) for(ll i=l;i<r;i++)
#define REP(i,n) FOR(i,0,n)
#define RFOR(i,l,r) for(ll i=r-1;i>=l;i--)
#define RREP(i,n) RFOR(i,0,n)
#define ALL(x) x.begin(),x.end()
#define P pair<ll,ll>
#define F first
#define S second
#define BS(A,x) binary_search(ALL(A),x)
#define LB(A,x) (ll)(lower_bound(ALL(A),x)-A.begin())
#define UB(A,x) (ll)(upper_bound(ALL(A),x)-A.begin())
#define COU(A,x) UB(A,x)-LB(A,x)
template<typename T>using min_priority_queue=priority_queue<T,vector<T>,greater<T>>;
//using mint=modint1000000007;
using mint=modint998244353;
void chmax(ll&a,ll b){a=max(a,b);}
void chmin(ll&a,ll b){a=min(a,b);}
signed main(){
  ll N;string S;cin>>N>>S;
  mint ans=0;
  if(S[0]>'a')ans+=pow_mod(25,N-1,998244353);
  if(N>1&&S[0]>'b')ans+=(S[0]-'b')*(N-1)*pow_mod(25,N-2,998244353);
  REP(i,N-1){
    if(S[i]=='a'){
      FOR(j,i+1,N){
        if(S[j]=='a')break;
        ans+=(S[j]-'b')*pow_mod(25,N-1-j,998244353);
      }
      break;
    }
    if(S[i+1]>'a'){
      ans+=pow_mod(25,N-2-i,998244353);
      if(i<N-2)ans+=(S[i+1]-'b')*(N-2-i)*pow_mod(25,N-3-i,998244353);
    }
  }
  cout<<ans.val()<<endl;
  return 0;
}