import sys, time, random
from collections import deque, Counter, defaultdict
input = lambda: sys.stdin.readline().rstrip()
ii = lambda: int(input())
mi = lambda: map(int, input().split())
li = lambda: list(mi())
inf = 2 ** 63 - 1
mod = 998244353
import string
s = string.ascii_lowercase
n, m, k = mi()
a = input()
dp = [[0] * (30) for _ in range(m + 2)]

S = set()
ans = -1
for i in range(m + 1):
    for j in range(27):
        dp[i + 1][j] += dp[i][j] * j
        dp[i + 1][j] %= mod
        dp[i + 1][j + 1] += dp[i][j] * (26-j)
        dp[i + 1][j + 1] %= mod
    L = len(S)
    if i < n:
        p = s.index(a[i])
        for to in range(0, p):
            if s[to] not in S:
                dp[i + 1][L + 1] += 1
            else:
                dp[i + 1][L] += 1
        S.add(a[i])
        if len(S) >= k:
            ans += 1
    for j in range(k, 27):
        ans += dp[i][j]
        ans %= mod
print(ans)