max_K = 10**6
MOD = 998244353
fact    =[-1] * (max_K+1) #MOD下での階乗
inv     =[-1] * (max_K+1) #MOD下での逆元
fact_inv=[-1] * (max_K+1) #MOD下での階乗の逆元
fact[0]=fact[1]=1
inv[1] = 1
fact_inv[0]=fact_inv[1] = 1
for i in range(2,max_K+1):
    fact[i] = (fact[i-1]*i)%MOD
    inv[i] = (-inv[MOD%i]*(MOD//i))%MOD
    fact_inv[i] = (fact_inv[i-1]*inv[i])%MOD

def comb(n,r,MOD):
    if n < r:
        return 0
    return fact[n]*fact_inv[n-r]%MOD*fact_inv[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,MOD)
    ans %= MOD
print(ans)