from collections import deque
mod = 998244353

N,K = map(int,input().split())
A = list(map(int,input().split()))
B = list(map(int,input().split()))

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

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