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 c = NList;
        var (n, m, k) = (c[0], c[1], c[2]);
        var s = ReadLine();
        var kinds = 26;
        WriteLine(Least(n, m, k, kinds, s));
    }
    static long Least(int n, int m, int k, int kinds, string s)
    {
        var ans = 0L;
        var mod = 998_244_353;
        var dp = new long[m][];
        for (var i = 0; i < dp.Length; ++i) dp[i] = new long[kinds + 1];
        var count = new int[kinds];
        for (var i = 0; i < m; ++i)
        {
            if (i == 0)
            {
                for (var si = 'a'; si < s[0]; ++si) ++dp[0][1];
            }
            else
            {
                for (var j = 1; j < dp[i].Length; ++j)
                {
                    dp[i][j] = (dp[i][j] + dp[i - 1][j] * j) % mod;
                    if (j + 1 < dp[i].Length) dp[i][j + 1] = (dp[i][j + 1] + dp[i - 1][j] * (kinds - j));
                }
                if (i < n)
                {
                    var kind = count.Count(ci => ci > 0);
                    for (var j = 0; j < s[i] - 'a'; ++j)
                    {
                        if (count[j] == 0) ++kind;
                        dp[i][kind] = (dp[i][kind] + 1) % mod;
                        if (count[j] == 0) --kind;
                    }
                }
            }
            if (i < n)
            {
                ++count[s[i] - 'a'];
            }
            if (i + 1 < n && count.Count(ci => ci > 0) >= k) ans = (ans + 1) % mod;
            for (var j = k; j < dp[i].Length; ++j) ans = (ans + dp[i][j]) % mod;
        }
        return ans;
    }
}