N,K = map(int,input().split())
S = input().strip()
MOD = 998244353
A = [1]*(N+1)
for i in range(2,N+1):
    A[i] = (A[i-1]*i) % MOD
B = [1]*(N+1)
B[N] = pow(A[N], MOD-2, MOD)
for i in range(N-1,1,-1):
    B[i] = (B[i+1]*(i+1)) % MOD
def comb(n,k):
    if n<k or k<0:return 0
    return (A[n]*B[k]*B[n-k]) % MOD
n = S.count("N")
nc = 0
for i in range(N-1):
    if S[i]=="C" and S[i+1]=="N":
        nc += 1
ans = 0
for i in range(1,n-max(K,nc)+1):
    ans = (ans+comb(n-nc,i))%MOD
print(ans)