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

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[] values = sc.next().toCharArray();
        long[][][] dp = new long[n + 1][2][2];
        dp[0][0][0] = 1;
        for (int i = 1; i <= n; i++) {
            if (values[i - 1] == 'a') {
                dp[i][1][0] = dp[i - 1][0][0];
                dp[i][0][1] = (dp[i - 1][0][1] * 25) % MOD;
                dp[i][1][1] = (dp[i - 1][1][1] * 25 + dp[i - 1][0][1]) % MOD;
            } else {
                dp[i][0][0] = dp[i - 1][0][0];
                dp[i][1][0] = dp[i - 1][1][0];
                dp[i][0][1] = (dp[i - 1][0][1] * 25 + dp[i - 1][0][0] * (values[i - 1] - 'b')) % MOD;
                dp[i][1][1] = (dp[i - 1][1][1] * 25 + dp[i - 1][0][1] + dp[i - 1][1][0] * (values[i - 1] - 'b') + dp[i - 1][0][0]) % MOD;
            }
        }
        System.out.println(dp[n][1][1]);
    }
}
class Scanner {
    BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
    StringTokenizer st = new StringTokenizer("");
    
    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 nextLine() throws Exception {
        return br.readLine();
    }
    
    public String next() throws Exception {
        if (!st.hasMoreTokens()) {
            st = new StringTokenizer(br.readLine());
        }
        return st.nextToken();
    }
}