R=range
J=lambda:map(int,input().split())
N,K=J()
A=list(J())+[0]
B=list(J())
a=0
t=[1]+[0]*N
P=998244353
for m in R(K-1,K+1):
	s=p=1
	for i in R(N):
		t[i+1]=s*B[i]%P;s=((s if i<m else s-p*t[i-m])*A[i]+t[i+1])%P;p=p*A[i]%P
		if i>=m:p=p*pow(A[i-m],-1,P)%P
	s=0;p=1
	for k in R(m+1):s+=t[N-k]*p;p=p*A[N-1-k]%P
	a+=[s,-s][m<K]
print(a%P)