n, m, k = gets.split.map(&:to_i)
s = gets.chomp

MODULO = 998244353
KMAX = 26
ORD_A = "a".ord

kbits, kbc, result = 0, 0, 0
dp = Array.new(KMAX + 2, 0)

def popcount32(x)
    x = ((x & 0xaaaaaaaa) >>  1) + (x & 0x55555555)
    x = ((x & 0xcccccccc) >>  2) + (x & 0x33333333)
    x = ((x & 0xf0f0f0f0) >>  4) + (x & 0x0f0f0f0f)
    x = ((x & 0xff00ff00) >>  8) + (x & 0x00ff00ff)
    x = ((x & 0xffff0000) >> 16) + (x & 0x0000ffff)
    x
end

s.bytes do |c|
	ci = c - ORD_A
	ndp = Array.new(KMAX + 2, 0)
	same = popcount32(kbits & ((1 << ci) - 1))
	(1..KMAX).each do |j|
		ndp[j] = ((KMAX - j + 1) * dp[j - 1] + j * dp[j]) % MODULO
	end
	ndp[kbc] += same
	ndp[kbc + 1] += ci - same
	if (kbits & (1 << ci)) == 0 then
		kbits |= (1 << ci)
		kbc += 1
	end
	if kbc >= k then
		result += 1
	end
	result += ndp[k..KMAX].sum
	dp = ndp
end

if kbc >= k then
	result -= 1
end

(n...m).each do |i|
	ndp = Array.new(KMAX + 2, 0)
	(1..KMAX).each do |j|
		ndp[j] = ((KMAX - j + 1) * dp[j - 1] + j * dp[j]) % MODULO
	end
	result += ndp[k..KMAX].sum
	dp = ndp
end

puts result % MODULO