#include <bits/stdc++.h>
#include <atcoder/all>
using namespace std;
using namespace atcoder;
//using mint = modint1000000007;
//const int mod = 1000000007;
using mint = modint998244353;
const int mod = 998244353;
//const int INF = 1e9;
//const long long LINF = 1e18;
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define rep2(i,l,r)for(int i=(l);i<(r);++i)
#define rrep(i, n) for (int i = (n) - 1; i >= 0; --i)
#define rrep2(i,l,r)for(int i=(r) - 1;i>=(l);--i)
#define all(x) (x).begin(),(x).end()
#define allR(x) (x).rbegin(),(x).rend()
#define P pair<int,int>
template<typename A, typename B> inline bool chmax(A & a, const B & b) { if (a < b) { a = b; return true; } return false; }
template<typename A, typename B> inline bool chmin(A & a, const B & b) { if (a > b) { a = b; return true; } return false; }

int main() {
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	int n, k; cin >> n >> k;
	vector<int>a(n), b(n);
	rep(i, n)cin >> a[i];
	rep(i, n)cin >> b[i];
	vector<mint>s(n + 1, 1), si(n + 1);
	rep(i, n)s[i + 1] = s[i] * a[i];
	si[n] = s[n].inv();
	rrep(i, n)si[i] = si[i + 1] * a[i];
	// f(k) := maxCombo < k
	auto f = [&](int k)->mint {
		std::vector<mint>dp0(n + 1), dp1(n + 1);
		dp1[0] = 1;
		rep(i, n + 1) {
			if (k <= i) {
				dp0[i] -= dp1[i - k] * s[i] * si[i - k];
			}
			if (i == n)break;
			dp0[i + 1] += (dp0[i] + dp1[i]) * a[i];
			dp1[i + 1] += (dp0[i] + dp1[i]) * b[i];
		}
		return dp0[n] + dp1[n];
	};
	mint ans = f(k + 1) - f(k);
	cout << ans.val() << endl;
	return 0;
}