N, K = map(int, input().split())
S = list(input())
mod = 998244353
n = 505050
fact = [1] * (n + 1)
invfact = [1] * (n + 1)
for i in range(1, n):
    fact[i + 1] = ((i+1) * fact[i]) % mod
invfact[n] = pow(fact[n], mod - 2, mod)
for i in range(n - 1, -1, -1):
    invfact[i] = invfact[i + 1] * (i + 1) % mod

def comb(n, r):
    if n < 0 or r < 0 or n - r < 0:
        return 0
    return fact[n] * invfact[r] * invfact[n - r] % mod

cnt = 0
flag = 0
for s in S:
    if s == "C":
        flag = 1
    elif s == "N":
        if not flag:
            cnt += 1
        else:
            K -= 1
        flag = 0
    else:
        flag = 0
        
ans = 0
for i in range(1, cnt - K + 1):
    ans += comb(cnt, i)
    ans %= mod
print(ans)