#include <bits/stdc++.h>
using namespace std;
#define ll long long int
#define mod 998244353
ll dp[200005][2][2];
string s;
int n;
ll solve(int pos,bool used,bool small){
	if(pos>=n){
		return (ll)(used&&small);

	}
	if(dp[pos][used][small]!=-1)
		return dp[pos][used][small];
	ll ans=0;

	char r=small?'z':s[pos];
	char l='a';
	if(used)
		l++;
	for(char c=l;c<=r;c++){
		ans+=solve(pos+1,(c=='a')|used,small|(c<r));
		ans%=mod;
	}
	return dp[pos][used][small]=ans;



}

int main() {
	
	int t=1;
	//cin>>t;
	assert(1<=t&&t<=10);
	while(t--){
		cin >> n >> s;
		assert(1<=n&&n<=200000);
		assert(s.size()==n);
		for(int i=0;i<n;i++){
			assert(s[i]>='a'&&s[i]<='z');
		}
		memset(dp,-1,sizeof(dp));
		cout<<solve(0,0,0)<<"\n";

	}
	
	
	
}