N, M, K = map(int, input().split())
S = input()
ORDA, kbits, kbc, result = ord('a'), 0, 0, 0
dp = [0] * 28
for i in range(M):
    ndp = [0] * 28
    for j in range(1, 27):
        ndp[j] = ((27 - j) * dp[j - 1] + j * dp[j]) % 998244353
    if i < N:
        ci = ord(S[i]) - ORDA
        cib = 1 << ci
        same = (kbits & (cib - 1)).bit_count()
        ndp[kbc] += same
        ndp[kbc + 1] += ci - same
        if (kbits & cib) == 0:
            kbits |= cib
            kbc += 1
        if kbc >= K:
            result += 1
    for j in range(K, 27):
        result += ndp[j]
    dp = ndp
if kbc >= K:
    result -= 1
print(result % 998244353)