import java.io.*;
import java.util.*;

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[] input = sc.next().toCharArray();
        long[][] dp = new long[n + 1][2];
        int aCount = 0;
        for (int i = 1; i <= n; i++) {
            dp[i][0] = dp[i - 1][0] * 25 % MOD;
            dp[i][1] = (dp[i - 1][0] + dp[i - 1][1] * 25) % MOD;
            if (input[i - 1] == 'a') {
                aCount++;
                continue;
            }
            if (aCount >= 2) {
                continue;
            }
            dp[i][aCount] += input[i - 1] - 'b';
            dp[i][aCount] %= MOD;
            if (aCount == 0) {
                dp[i][1]++;
                dp[i][1] %= MOD;
            }
        }
        System.out.println(dp[n][1]);
    }
}
    
class Scanner {
    BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
    StringTokenizer st = new StringTokenizer("");
    StringBuilder sb = new StringBuilder();
    
    public Scanner() throws Exception {
        
    }
    
    public int nextInt() throws Exception {
        return Integer.parseInt(next());
    }
    
    public long nextLong() throws Exception {
        return Long.parseLong(next());
    }
    
    public double nextDouble() throws Exception {
        return Double.parseDouble(next());
    }
    
    public String next() throws Exception {
        while (!st.hasMoreTokens()) {
            st = new StringTokenizer(br.readLine());
        }
        return st.nextToken();
    }
    
}