import java.io.*;
import java.util.*;
import java.util.function.*;
import java.util.stream.*;

public class Main {
    static final int MOD = 998244353;
    public static void main(String[] args) throws Exception {
        Scanner sc = new Scanner();
        int n = sc.nextInt();
        char[] inputs = sc.next().toCharArray();
        int length = inputs.length;
        long[][] dp = new long[length][2];
        int aCount = 0;
        if (inputs[0] == 'a') {
            aCount = 1;
        } else {
            dp[0][0] = inputs[0] - 'b';
            dp[0][1] = 1;
        }
        for (int i = 1; i < length; i++) {
            int x = inputs[i] - 'a';
            dp[i][0] = dp[i - 1][0] * 25 % MOD;
            dp[i][1] = (dp[i - 1][0] + dp[i - 1][1] * 25) % MOD;
            if (aCount == 0) {
                if (x > 0) {
                    dp[i][0] += x - 1;
                    dp[i][0] %= MOD;
                    dp[i][1]++;
                    dp[i][1] %= MOD;
                }
            } else if (aCount == 1) {
                if (x > 0) {
                    dp[i][1] += x - 1;
                    dp[i][1] %= MOD;
                }
            }
            if (x == 0) {
                aCount++;
            }
        }
        System.out.println(dp[length - 1][1]);
    }
}
class Scanner {
    BufferedReader br;
    StringTokenizer st = new StringTokenizer("");
    StringBuilder sb = new StringBuilder();
    
    public Scanner() {
        try {
            br = new BufferedReader(new InputStreamReader(System.in));
        } catch (Exception e) {
            
        }
    }
    
    public int nextInt() {
        return Integer.parseInt(next());
    }
    
    public long nextLong() {
        return Long.parseLong(next());
    }
    
    public double nextDouble() {
        return Double.parseDouble(next());
    }
    
    public String next() {
        try {
            while (!st.hasMoreTokens()) {
                st = new StringTokenizer(br.readLine());
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            return st.nextToken();
        }
    }
    
}