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

MODULO = 998244353
KMAX = 26

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

s.bytes do |c|
	ci = c - "a".ord
	ndp.fill(0)
	same = (kbits & ((1 << ci) - 1)).to_s(2).count('1')
	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
	(1..KMAX).each do |j|
		ndp[j] += j * dp[j]
		ndp[j + 1] += (KMAX - j) * dp[j]
		ndp[j] %= MODULO
	end
	(k..KMAX).each do |j|
		result += ndp[j]
	end
	dp, ndp = ndp, dp
end

if kbc >= k then
	result -= 1
end

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

puts result % MODULO