fact=[]
rev=[]
def comb_init(N=1000000,MOD=998244353):
    global fact,rev
    fact=[1]
    rev=[1]
    for i in range(N):
        fact.append((fact[-1]*(i+1))%MOD)
        rev.append((rev[-1]*pow(i+1,MOD-2,MOD))%MOD)

def comb(n,r,MOD=998244353):
    if n<r:
        return 0
    return (fact[n]*rev[r]*rev[n-r])%MOD

comb_init()
N,K=map(int,input().split())
S="P"+input()
cnt=0
for i in range(N):
	if S[i+1]=="N":
		if S[i]!="C":
			cnt+=1
		else:
			K-=1
ans=0
for i in range(1,cnt-K+1):
	ans+=comb(cnt,i)
print(ans%998244353)