import java.util.*;

public class Main {
    
    public static void main(String[] args) throws Exception {
        
        Scanner sc = new Scanner(System.in);
        int N = sc.nextInt();
        char[] s = sc.next().toCharArray();
        int[][][] dp = new int[N][2][2];
        int mod = 998244353;
        for( int i = 0; i <= s[0]-'a'; i++ ) {
            int j = i == 0 ? 1 : 0;
            int k = i < s[0]-'a' ? 1 : 0;
            dp[0][j][k]++;
        }
        
        for( int i = 0; i < N-1; i++ ) {
            for( int j = 0; j <= 1; j++ ) {
                for( int k = 0; k <= 1; k++ ) {
                    int max = k == 1 ? 'z'-'a' : s[i+1]-'a';
                    for( int d = 0; d <= max; d++ ) {
                        int x = d == 0 ? 1 : 0;
                        int y = d < s[i+1]-'a' ? 1 : 0;
                        if( (j&x) == 1 ) continue;
                        dp[i+1][j|x][k|y] += dp[i][j][k];
                        dp[i+1][j|x][k|y] %= mod;
                    }
                }
            }
        }
        
        System.out.println(dp[N-1][1][1]);
        
    }
    
}