#include <stdio.h>
#include <bits/stdc++.h>
#include <atcoder/all>
using namespace atcoder;
using mint = modint998244353;
using namespace std;
#define rep(i,n) for (int i = 0; i < (n); ++i)
#define Inf32 1000000001
#define Inf64 1000000000000000001

mint sol(int N,int K,vector<mint> a,vector<mint> b){
	if(K==0){
		mint r = 1;
		rep(i,b.size())r *= b[i];
		return r;
	}
	vector<mint> dp(N+2,0);
	dp[0] = 1;
	b.push_back(1);
	a.push_back(0);
	N++;
	mint sum = dp[0];
	mint mul = 1;
	rep(i,N){
		dp[i+1] = sum * b[i];
		if(i-K>=0){
			sum -= dp[i-K] * mul;
			mul /= a[i-K];
		}
		sum *= a[i];
		sum += dp[i+1];
		mul *= a[i];
	}
	return dp.back();
}
int main(){
	int N,K;
	cin>>N>>K;
	vector<mint> a(N),b(N);
	rep(i,N){
		int t;
		cin>>t;
		a[i] = t;
	}
	rep(i,N){
		int t;
		cin>>t;
		b[i] = t;		
	}
	
	mint ans = sol(N,K,a,b);
	ans -= sol(N,K-1,a,b);
	cout<<ans.val()<<endl;
    return 0;
}