#TLE解法です。
import math
MOD = 998244353
def comb(n,r):
    return math.comb(n,r)%MOD

N,K = map(int,input().split())
S = input()
tmp = 0
hima = 0
for i in range(N):
    if i != 0:
        if S[i] == "N" and S[i-1] != "C":
            tmp += 1
    else:
        if S[i] == "N":
            tmp += 1
    if S[i] == "N":
        hima += 1
ans = 0
for i in range(1,hima-K+1):
    ans += comb(tmp,i)
    ans %= MOD
print(ans)