import sys

n, m, k = map(int, input().split())
s = input()

MOD = 998244353
KMAX = 26
KMAX2 = KMAX + 2
ORDA = ord('a')
kbits = 0
kbc = 0
result = 0
dp = [0] * KMAX2

if len(s) != n or n < 1 or n > m or m > 500000 or k < 1 or k > KMAX:
    sys.exit(1)

for c in s:
    ndp = [0] * KMAX2
    ci = ord(c) - ORDA
    if ci < 0 or ci >= KMAX:
        sys.exit(1)
    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(1, KMAX + 1):
        ndp[j] += j * dp[j]
        ndp[j + 1] += (KMAX - j) * dp[j]
        ndp[j] %= MOD
    for j in range(k, KMAX + 1):
        result += ndp[j]
    dp = ndp

if kbc >= k:
    result -= 1

for _ in range(n, m):
    ndp = [0] * KMAX2
    for j in range(1, KMAX + 1):
        ndp[j] += j * dp[j]
        ndp[j + 1] += (KMAX - j) * dp[j]
        ndp[j] %= MOD
    for j in range(k, KMAX + 1):
        result += ndp[j]
    dp = ndp

result %= MOD
print(result)