import sys

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

MOD = 998244353
KMAX = 26
kbits = 0
result = 0
dp = [0] * KMAX

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

if kbits.bit_count() >= k:
    result -= 1
    result %= MOD

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

print(result)