#include<bits/stdc++.h>
namespace {
#pragma GCC diagnostic ignored "-Wunused-function"
#include<atcoder/all>
#pragma GCC diagnostic warning "-Wunused-function"
using namespace std;
using namespace atcoder;
#define rep(i,n) for(int i = 0; i < (int)(n); i++)
#define rrep(i,n) for(int i = (int)(n) - 1; i >= 0; i--)
#define all(x) begin(x), end(x)
#define rall(x) rbegin(x), rend(x)
template<class T> bool chmax(T& a, const T& b) { if (a < b) { a = b; return true; } else return false; }
template<class T> bool chmin(T& a, const T& b) { if (b < a) { a = b; return true; } else return false; }
using ll = long long;
using P = pair<int,int>;
using VI = vector<int>;
using VVI = vector<VI>;
using VL = vector<ll>;
using VVL = vector<VL>;
using mint = modint998244353;

} int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  int n, k;
  cin >> n >> k;
  VI a(n), b(n);
  rep(i, n) cin >> a[i];
  rep(i, n) cin >> b[i];
  vector<mint> pa(n + 1, 1), pa_inv(n + 1);
  rep(i, n) pa[i + 1] = pa[i] * a[i];
  pa_inv[n] = pa[n].inv();
  rrep(i, n) pa_inv[i] = pa_inv[i + 1] * a[i];
  mint ans;
  rep(z, 2) {
    vector<mint> add(n + 1), start(n + 1);
    start[0] = 1;
    mint now;
    rep(i, n + 1) {
      now += start[i] + add[i];
      if (i + k + 1 <= n) add[i + k + 1] -= start[i] * pa[i + k + 1] * pa_inv[i];
      if (i == n) break;
      start[i + 1] += now * b[i];
      now *= a[i];
    }
    if (z == 0) ans += now;
    else ans -= now;
    k--;
  }
  cout << ans.val() << '\n';
}