#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() {
	cin >> n >> s;
	
	memset(dp,-1,sizeof(dp));
	cout<<solve(0,0,0);
	
	
}