mod = 998244353

N,K = map(int,input().split())
A = list(map(int,input().split()))
B = list(map(int,input().split()))
inv_A = [pow(A[i],mod - 2,mod) for i in range(N)]

def solve(k):
  P = [0] * (N + K + 5)
  P[-1] = 1
  Q = 1
  S = 1
  for i in range(N):
    a,b = A[i],B[i]
    p = inv_A[i] * S % mod
    p = p * b % mod
    P[i] = p
    S = (S + p) % mod
    q = P[i - k - 1]
    S = (S - q) % mod
    Q = Q * a % mod
  return S * Q % mod

ans = (solve(K) - solve(K - 1)) % mod
print(ans)