#ifndef ONLINE_JUDGE
#define _GLIBCXX_DEBUG
#endif
#include "atcoder/all"
#include <string>
#include <bits/stdc++.h>
#include <climits>
#include <boost/multiprecision/cpp_dec_float.hpp>
#include <boost/multiprecision/cpp_int.hpp>
#include <boost/rational.hpp>
#include <boost/functional/hash.hpp>
// 任意長整数型
using Bint = boost::multiprecision::cpp_int;
// 仮数部が10進数で1024桁の浮動小数点数型(TLEしたら小さくする)
using BReal =
    boost::multiprecision::number<boost::multiprecision::cpp_dec_float<1024>>;
using Rat = boost::rational<Bint>;
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
#include <concepts>
#include <functional>
using namespace std;
using namespace __gnu_pbds;
// 型エイリアスの設定
template<typename T>
using ordered_set = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
using namespace atcoder;
template<class T> inline bool chmax(T& a, T b) { if (a < b) { a = b; return 1; } return 0; }
template<typename T> inline bool chmin(T &a, T b) { return ((a>b) ? (a = b, true) : (false));}
#define rep(i,n) for(int i=0;i<(int)(n);i++)
#define drep(i,n) for(int i=n-1;i>=0;i--)
#define REP(i,s,n) for(int i=s;i<(int)n;i++)
#define DREP(i,s,n) for(int i=n-1;i>=s;i--)
const long long inf = 1LL<<60;
const int infi = 1e9+1;
typedef long long ll;
typedef long double ld;
typedef __int128_t l3;
//cmpArg := 偏角ソート, atan2l(y, x); atan2l(y, x) = [-pi, pi]
#define cmpArg [](const auto &p1, const auto &p2) { return atan2l(p1.second, p1.first) < atan2l(p2.second, p2.first); }
typedef pair<int,int> pi;
typedef pair<ll,ll> pl;
typedef unsigned long long ull;
#define vl vector<ll>
#define vvl vector<vector<ll>>
#define vi vector<int>
#define vvi vector<vector<int>>
#define vm vector<mint>
#define vvm vector<vector<mint>>
#define vvc vector<vector<char>>
#define vc vector<char>
#define vvpi vector<vector<pi>>
#define vpi vector<pi>
#define vpl vector<pl>
#define vvpl vector<vector<pl>>
#define pb push_back
#define eb emplace_back
#define YES cout<<"Yes"<<endl;
#define NO cout<<"No"<<endl;
#define YN { cout << "Yes" << endl; } else { cout << "No" << endl; }
#define all(x) x.begin(), x.end()
#define rall(i) std::rbegin(i), std::rend(i)
#define len(x) ((ll)(x).size())
#define fi first
#define se second
#define UNIQUE(x) sort(all(x)), x.erase(unique(all(x)), x.end())
int pc(ll x) { return __builtin_popcount(x); } //ビット列にどれだけ1がたっているかを求める pop count
void cincout(){  ios::sync_with_stdio(false);   std::cin.tie(nullptr);  cout<< fixed << setprecision(15);  }
bool out_grid(ll i, ll j, ll h, ll w) { return (!(0<=i && i<h && 0<=j && j<w)); }
inline void read(int &a) { std::cin >> a; }
inline void read(unsigned &a) { std::cin >> a; }
inline void read(long &a) { std::cin >> a; }
inline void read(long long &a) { std::cin >> a; }
inline void read(unsigned long long &a) { std::cin >> a; }
inline void read(char &a) { std::cin >> a; }
inline void read(float &a) { std::cin >> a; }
inline void read(double &a) { std::cin >> a; }
inline void read(long double &a) { std::cin >> a; }
inline void read(std::vector<bool> &vec) {
    for (int32_t i = 0; i < vec.size(); i++) {
        int a;
        read(a);
        vec[i] = a;
    }
}
inline void read(std::string &a) { std::cin >> a; }
template <class T>
inline void read(std::vector<T> &vec);
template <class T, size_t size>
inline void read(std::array<T, size> &vec);
template <class T, class L>
inline void read(std::pair<T, L> &p);
template <class T, size_t size>
inline void read(T (&vec)[size]);
template <class T>
inline void read(std::vector<T> &vec) {
    for (auto &i : vec) read(i);
}
template <class T>
inline void read(std::deque<T> &vec) {
    for (auto &i : vec) read(i);
}
template <class T, size_t size>
inline void read(std::array<T, size> &vec) {
    for (auto &i : vec) read(i);
}
template <class T, class L>
inline void read(std::pair<T, L> &p) {
    read(p.first);
    read(p.second);
}
template <class T, size_t size>
inline void read(T (&vec)[size]) {
    for (auto &i : vec) read(i);
}
template <class T>
inline void read(T &a) {
    std::cin >> a;
}
inline void in() {}
template <class Head, class... Tail>
inline void in(Head &head, Tail &...tail) {
    read(head);
    in(tail...);
}
inline void print() { std::cout << ' '; }
inline void print(const bool &a) { std::cout << a; }
inline void print(const int &a) { std::cout << a; }
inline void print(const unsigned &a) { std::cout << a; }
inline void print(const long &a) { std::cout << a; }
inline void print(const long long &a) { std::cout << a; }
inline void print(const unsigned long long &a) { std::cout << a; }
inline void print(const char &a) { std::cout << a; }
inline void print(const char a[]) { std::cout << a; }
inline void print(const float &a) { std::cout << a; }
inline void print(const double &a) { std::cout << a; }
inline void print(const long double &a) { std::cout << a; }
inline void print(const std::string &a) {
    for (auto &&i : a) print(i);
}
template <class T>
inline void print(const std::vector<T> &vec);
template <class T, size_t size>
inline void print(const std::array<T, size> &vec);
template <class T, class L>
inline void print(const std::pair<T, L> &p);
template <class T, size_t size>
inline void print(const T (&vec)[size]);
template <class T>
inline void print(const std::vector<T> &vec) {
    if (vec.empty()) return;
    print(vec[0]);
    for (auto i = vec.begin(); ++i != vec.end();) {
        std::cout << ' ';
        print(*i);
    }
}
template <class T>
inline void print(const std::deque<T> &vec) {
    if (vec.empty()) return;
    print(vec[0]);
    for (auto i = vec.begin(); ++i != vec.end();) {
        std::cout << ' ';
        print(*i);
    }
}
template <class T, size_t size>
inline void print(const std::array<T, size> &vec) {
    print(vec[0]);
    for (auto i = vec.begin(); ++i != vec.end();) {
        std::cout << ' ';
        print(*i);
    }
}
template <class T, class L>
inline void print(const std::pair<T, L> &p) {
    print(p.first);
    std::cout << ' ';
    print(p.second);
}
template <class T, size_t size>
inline void print(const T (&vec)[size]) {
    print(vec[0]);
    for (auto i = vec; ++i != end(vec);) {
        std::cout << ' ';
        print(*i);
    }
}
template <class T>
inline void print(const T &a) {
    std::cout << a;
}
inline void out() { std::cout << '\n'; }
template <class T>
inline void out(const T &t) {
    print(t);
    std::cout << '\n';
}
template <class Head, class... Tail>
inline void out(const Head &head, const Tail &...tail) {
    print(head);
    std::cout << ' ';
    out(tail...);
}
#define vec(type, name, ...) vector<type> name(__VA_ARGS__);
#define vv(type, name, h, ...) std::vector<std::vector<type>> name(h, std::vector<type>(__VA_ARGS__));
#define INT(...) int32_t __VA_ARGS__; in(__VA_ARGS__)
#define LL(...) int64_t __VA_ARGS__; in(__VA_ARGS__)
#define ULL(...) uint64_t __VA_ARGS__; in(__VA_ARGS__)
#define STR(...) std::string __VA_ARGS__; in(__VA_ARGS__)
#define CHR(...) char __VA_ARGS__; in(__VA_ARGS__)
#define LD(...) long double __VA_ARGS__; in(__VA_ARGS__)
#define VEC(type, name, size) std::vector<type> name(size); in(name)
#define VV(type, name, h, w) std::vector<std::vector<type>> name(h, std::vector<type>(w)); in(name)
template <class T>
ll sum(const T &a) {
    return accumulate(std::begin(a), std::end(a), 0LL);
}
template <class T>
ld dsum(const T &a) {
    return accumulate(std::begin(a), std::end(a), 0.0L);
}
template <class T>
auto min(const T &a) {
    return *min_element(std::begin(a), std::end(a));
}
template <class T>
auto max(const T &a) {
    return *max_element(std::begin(a), std::end(a));
}
template<typename T> T floor_div(const T n, const T d) {
    assert(d != 0);
    return n / d - static_cast<T>((n ^ d) < 0 && n % d != 0);
}
template<typename T> T ceil_div(const T n, const T d) {
    assert(d != 0);
    return n / d + static_cast<T>((n ^ d) >= 0 && n % d != 0);
}

using mint = modint998244353;

int main()
{
    INT(N,K);
    VEC(int,A,N); VEC(int,B,N); A.pb(0); B.pb(1); N++;
    vm proc(N+1,1); rep(i,N) proc[i+1] = proc[i] * A[i];
    auto get =[&](int l, int r) -> mint { return proc[r] / proc[l]; }; //[l,r)の総積をとる
    vm inv(N,1); rep(i,N-1) inv[i+1] = inv[i] / A[i];
    auto get_inv = [&](int l, int r) -> mint { return inv[r] / inv[l]; };

    vector<deque<mint>> dqs(2); dqs[0].pb(1), dqs[1].pb(0);
    vm sum(2,0); sum[0] = 1; sum[1] = 0;
    vvm dp(N+1,vm(2,0)); dp[0][0] = 1;
    rep(i,N) {
        //ぬく
        while(len(dqs[0]) > K) {
            mint val = dqs[0].front(); dqs[0].pop_front();
            sum[0] -= val;
        }
        while(len(dqs[1]) > K+1) {
            mint val = dqs[1].front(); dqs[1].pop_front();
            sum[1] -= val;
        }
        //dp更新
        dp[i+1][0] += sum[0]*B[i]*get(0,i);
        dp[i+1][1] += sum[1]*B[i]*get(0,i); if(i-K>=0) dp[i+1][1] += dp[i-K][0] * get(i-K,i) * B[i];
        //deque更新
        if(i!=N-1) { sum[0] += dp[i+1][0] * get_inv(0,i+1); dqs[0].pb(dp[i+1][0]*get_inv(0,i+1)); }
        if(i!=N-1) { sum[1] += dp[i+1][1] * get_inv(0,i+1); dqs[1].pb(dp[i+1][1]*get_inv(0,i+1)); }
    }
    out(dp[N][1].val());
}