import sys
input = sys.stdin.readline

mod = 998244353
N, M, K = map(int, input().split())
S = input().rstrip()
dp = [[0] * 27 for _ in range(M+1)]
ch = set()
ans = 0
for i in range(M):
    for j in range(1, 27):
        dp[i+1][j] = (dp[i][j-1] * (27 - j) + dp[i][j] * j) % mod
    if i < N:
        if len(ch) >= K:
            ans += 1
        for c in range(ord(S[i]) - ord('a')):
            k = len(ch)
            if c not in ch:
                k += 1
            dp[i+1][k] += 1
        ch.add(ord(S[i]) - ord('a'))
ans += sum(dp[i][j] for i in range(1, M+1) for j in range(K, 27))
print(ans % mod)