#include <bits/stdc++.h>
#include <atcoder/modint>
using mint = atcoder::modint998244353;
using namespace std;


int main(){
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    
    int N, K;
    cin >> N >> K;
    vector<int> A(N), B(N);
    for (auto &a : A) cin >> a;
    for (auto &b : B) cin >> b;
    vector<mint> S(N + 1, 1), Si(N + 1);
    for (int i = 0; i < N; i++) S[i + 1] = S[i] * A[i];
    Si[N] = S[N].inv();
    for (int i = N; i > 0; i--) Si[i - 1] = Si[i] * A[i - 1];
    auto f = [&](int k) -> mint {
        std::vector<mint> dp0(N + 1), dp1(N + 1);
        dp1[0] = 1;
        for (int i = 0; i <= N; i++){
            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];
    };
    cout << (f(K + 1) - f(K)).val() << "\n";
}