class SegTree:
    def __init__(self, op, e, n, v=None):
        self._n = n
        self._op = op
        self._e = e
        self._log = (n - 1).bit_length()
        self._size = 1 << self._log
        self._d = [self._e] * (2 * self._size)
        if v is not None:
            for i in range(self._n):
                self._d[self._size + i] = v[i]
            for i in range(self._size - 1, 0, -1):
                self._update(i)
    
    def set(self, p, x):
        assert 0 <= p < self._n
        p += self._size
        self._d[p] = x
        for i in range(1, self._log + 1):
            self._update(p >> i)
    
    def get(self, p):
        assert 0 <= p < self._n
        return self._d[p + self._size]
 
    def prod(self, l, r):
        assert 0 <= l <= r <= self._n
        sml, smr = self._e, self._e
        l += self._size
        r += self._size
        while l < r:
            if l & 1:
                sml = self._op(sml, self._d[l])
                l += 1
            if r & 1:
                r -= 1
                smr = self._op(self._d[r], smr)
            l >>= 1
            r >>= 1
        return self._op(sml, smr)
    
    def all_prod(self):
        return self._d[1]
 
    def _update(self, k):
        self._d[k] = self._op(self._d[2 * k], self._d[2 * k + 1])
#https://qiita.com/AkariLuminous/items/32cbf5bc3ffb2f84a898からお借りしています。
N,K=list(map(int,input().split()))
A=list(map(int,input().split()))
B=list(map(int,input().split()))
A.append(0)
B.append(1)
def MUL(a,b):
	return (a*b)%998244353
STST=SegTree(MUL,1,N,A)
MOD=998244353
dp=[0]*(N+2)#Kコンボ未満
dp2=[0]*(N+2)#最大コンボがK
rui=1
dp[0]=1

for i in range(1,N+2):
  if i>=K+1:
    rui=(rui-STST.prod(i-K-1,i-1)*dp[i-K-1])%MOD #K+1ノーツ目でミスするときはフルコンボ(0ノーツ目でミス)はつなげてはいけない。それ以降も同様
  dp[i]=(rui*B[i-1])%MOD #iノーツ目でミス
  rui=(rui*A[i-1])%MOD #iノーツ目をつないだ(コンボ数+1)
  rui=(rui+dp[i])%MOD #0コンボ

rui=0#dp[i]と同様
for i in range(N+2):
  if i>=K+2:
    rui=(rui-STST.prod(i-K-2,i-1)*dp2[i-K-2])%MOD
  dp2[i]=(rui*B[i-1])%MOD
  if i>=K+1:
    dp2[i]=(dp2[i]+B[i-1]*STST.prod(i-K-1,i-1)*dp[i-K-1])%MOD
  rui=(rui*A[i-1])%MOD
  rui=(rui+dp2[i])%MOD
print(dp2[N+1])