#line 1 "era.cpp"
#include <bits/stdc++.h>
#include <atcoder/modint>
#line 4 "/Users/Shared/po167_library/ds/Swag.hpp"

namespace po167{
template<class T, T (*op)(T, T), T (*e)()>
struct SWAG
{
    std::vector<std::pair<T, T>> A, B;
    SWAG(int n = -1){
        if (n > 0) A.reserve(n + 1), B.reserve(n + 1);
        A.push_back({e(), e()});
        B.push_back({e(), e()});
    }
    void push(T v){
        B.push_back({v, op(B.back().second, v)});
    }
    void pop(){
        if ((int)A.size() == 1){
            while ((int)B.size() != 1){
                A.push_back({B.back().first, op(B.back().first, A.back().second)});
                B.pop_back();
            }
        }
        assert((int)A.size() != 1);
        A.pop_back();
    }
    T calc(){
        return op(A.back().second, B.back().second);
    }
};
}
#line 4 "era.cpp"
using mint = atcoder::modint998244353;
using namespace std;

mint op(mint a, mint b){
    return a * b;
}
mint e(){
    return 1;
}

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;
    auto f = [&](int k) -> mint {
        po167::SWAG<mint, op, e> S(k + 1);
        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.calc();
                S.pop();
            }
            if (i == N) break;
            S.push(A[i]);
            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";
}