N, K = map(int, input().split())
MOD = 998244353
fact = [1] * (N + 1)
rfact = [1] * (N + 1)
r = 1
for i in range(1, N + 1):
    fact[i] = r = r * i % MOD
rfact[N] = r = pow(fact[N], MOD - 2, MOD)
for i in range(N, 0, -1):
    rfact[i - 1] = r = r * i % MOD

# nCk (mod MOD) を求める
def comb(n, k):
    return fact[n] * rfact[k] * rfact[n - k] % MOD

S = input()
n = 0
cn = 0
for i in range(N):
    if S[i] == "N":
        if i > 0 and S[i - 1] == "C":
            cn += 1
        else:
            n += 1
K = max(K - cn, 0)
ans = 0
if n > K:
    for i in range(1, n - K + 1):
        ans += comb(n, i)
        ans %= MOD
print(ans)