from functools import cache
MOD = 998244353

N, K = map(int, input().split())
S = ['P'] + list(input())

@cache
def fact(n):
    if n == 0:
        return 1
    return fact(n-1) * n % MOD

@cache
def inv_fact(n):
    return pow(fact(n), -1, MOD)

def comb(n, r):
    return fact(n) * inv_fact(n-r) * inv_fact(r) % MOD

max_plan = S.count('N') - K
cnt = sum(1 for i in range(1, N+1) if S[i] == 'N' and S[i-1] != 'C')
print(sum(comb(cnt, i) for i in range(1, min(max_plan, cnt) + 1)) % MOD)