using System;
using static System.Console;
using System.Linq;
using System.Collections.Generic;

class Program
{
    static int NN => int.Parse(ReadLine());
    static int[] NList => ReadLine().Split().Select(int.Parse).ToArray();
    public static void Main()
    {
        Solve();
    }
    static void Solve()
    {
        var n = NN;
        var s = ReadLine();
        var mod = 998_244_353;
        var dp = new long[n + 1][];
        for (var i = 0; i < dp.Length; ++i) dp[i] = new long[4];
        dp[0][2] = 1;
        for (var i = 0; i < n; ++i)
        {
            dp[i + 1][0] = (dp[i + 1][0] + dp[i][0] * 25) % mod;
            dp[i + 1][1] = (dp[i + 1][1] + dp[i][0] + dp[i][1] * 25) % mod;
            if (s[i] == 'a')
            {
                dp[i + 1][3] = dp[i][2];
            }
            else
            {
                dp[i + 1][0] = (dp[i + 1][0] + dp[i][2] * (s[i] - 'b')) % mod;
                dp[i + 1][1] = (dp[i + 1][1] + dp[i][2] + dp[i][3] * (s[i] - 'b')) % mod;
                dp[i + 1][2] = dp[i][2];
                dp[i + 1][3] = dp[i][3];
            }
        }
        WriteLine(dp[n][1]);
    }
}