import sys

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

MOD = 998244353
KMAX = 26
kbits = 0
result = 0
dp = [0] * (KMAX + 2)

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 + 2)
	ci = ord(c) - ord('a')
	if ci < 0 or ci >= KMAX:
		sys.exit(1)
	kbc = kbits.bit_count()
	same = (kbits & ((1 << ci) - 1)).bit_count()
	ndp[kbc] += same
	ndp[kbc + 1] += ci - same
	kbits |= (1 << ci)
	if kbits.bit_count() >= k:
		result += 1
	for j in range(1, KMAX + 1):
		ndp[j] += j * dp[j]
		ndp[j + 1] += (KMAX - j) * dp[j]
	for j in range(KMAX + 1):
		ndp[j] %= MOD
	for j in range(k, KMAX + 1):
		result += ndp[j]
	result %= MOD
	dp = ndp

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

for _ in range(n, m):
	ndp = [0] * (KMAX + 2)
	for j in range(1, KMAX + 1):
		ndp[j] += j * dp[j]
		ndp[j + 1] += (KMAX - j) * dp[j]
	for j in range(KMAX + 1):
		ndp[j] %= MOD
	for j in range(k, KMAX + 1):
		result += ndp[j]
	result %= MOD
	dp = ndp

print(result)