import sys
input = sys.stdin.readline

N,K=map(int,input().split())
S=input().strip()

mod=998244353

FACT=[1]
for i in range(1,4*10**5+1):
    FACT.append(FACT[-1]*i%mod)

FACT_INV=[pow(FACT[-1],mod-2,mod)]
for i in range(4*10**5,0,-1):
    FACT_INV.append(FACT_INV[-1]*i%mod)

FACT_INV.reverse()

def Combi(a,b):
    if 0<=b<=a:
        return FACT[a]*FACT_INV[b]%mod*FACT_INV[a-b]%mod
    else:
        return 0


count=0
yasumi=0

for i in range(N):
    if S[i]=="N":
        yasumi+=1
        if i-1>=0 and S[i-1]=="C":
            pass
        else:
            count+=1

MAX=yasumi-K

ANS=0

for i in range(1,MAX+1):
    ANS=ANS+Combi(count,i)
    ANS%=mod

print(ANS)