#include <bits/stdc++.h>
using namespace std;

long long mod = 998244353;
//入力が必ずmod未満の時に使う.
struct mint{
    long long v = 0;
    mint(){} mint(int a){v = a;} mint(long long a){v = a;} mint(unsigned long long a){v = a;}
    long long val(){return v;}
    void modu(){v %= mod;}
 
    mint repeat2mint(const long long a,long long b){
        mint ret = 1,p = a;
        while(b){
            if(b&1) ret *= p;
            p *= p; b >>= 1;
        }
        return ret;
    };
 
    mint operator+(const mint b){return mint(v)+=b;}
    mint operator-(const mint b){return mint(v)-=b;}
    mint operator*(const mint b){return mint(v)*=b;}
    mint operator/(const mint b){return mint(v)/=b;}
 
    mint operator+=(const mint b){
        v += b.v; if(v >= mod) v -= mod;
        return *this;
    }
    mint operator-=(const mint b){
        v -= b.v; if(v < 0) v += mod; 
        return *this;
    }   
    mint operator*=(const mint b){v = v*b.v%mod; return *this;}
    mint operator/=(mint b){
        if(b == 0) assert(false);
        int left = mod-2;
        while(left){if(left&1) *this *= b; b *= b; left >>= 1;}
        return *this;
    }
 
    mint operator++(int){*this += 1; return *this;}
    mint operator--(int){*this -= 1; return *this;}
    bool operator==(const mint b){return v == b.v;}
    bool operator!=(const mint b){return v != b.v;}
    bool operator>(const mint b){return v > b.v;}
    bool operator>=(const mint b){return v >= b.v;}
    bool operator<(const mint b){return v < b.v;}
    bool operator<=(const mint b){return v <= b.v;}
    
    mint pow(const long long x){return repeat2mint(v,x);}
    mint inv(){return mint(1)/v;}
};

using SS = mint;
class SegmentTree{
    public:
    int siz = 1,n;
    vector<SS> dat;
 
    SS op(SS a, SS b){return a*b;}
    SS e(){return 1;}
    void renew (SS &a,SS x){
        //a = op(a,x);
        a = x;
        //その他.
    }
 
    void make(int N){
        while(siz < N) siz *= 2;
        n = N; dat.resize(siz*2,e());
    }
 
    void make2(int N,vector<SS> &A){
        make(N);
        for(int i=0; i<N; i++){
            int pos = i+siz;
            dat.at(pos) = A.at(i);
        }
        for(int i=siz-1; i>0; i--) dat.at(i) = op(dat.at(i*2),dat.at(i*2+1));
    }
 
    void update(int pos,SS x){
        pos = pos+siz;
        renew(dat.at(pos),x);
        while(pos != 1){
            pos = pos/2;
            dat.at(pos) = op(dat.at(pos*2),dat.at(pos*2+1));
        }
    }
 
    SS findans(int l, int r){
        SS retl = e(),retr = e();
        l += siz,r += siz;
        while(l < r){
            if(l&1) retl = op(retl,dat.at(l++));
            if(r&1) retr = op(dat.at(--r),retr);
            l >>= 1; r >>= 1;
        }
        return op(retl,retr);
    }
 
    SS get(int pos){return dat.at(pos+siz);}
    SS rangeans(int l, int r){return findans(l,r);}
    SS allrange(){return dat.at(1);}
 
    //rightは) leftは[で 渡す&返す. 
    int maxright(const function<bool(SS)> f,int l = 0){
        l += siz; int r = n+siz;
        vector<int> ls,rs;
        while(l < r){
            if(l&1) ls.push_back(l++);
            if(r&1) rs.push_back(--r);
            l >>= 1; r >>= 1; 
        }
        SS okl = e();
        for(int i=0; i<ls.size(); i++){
            l = ls.at(i);
            SS now = op(okl,dat.at(l));
            if(!f(now)){
                while(l < siz){
                    l <<= 1;
                    now = op(okl,dat.at(l));
                    if(f(now)){okl = now; l++;}
                }
                return l-siz;
            } 
            okl = now;
        }
        for(int i=rs.size()-1; i>=0; i--){
            l = rs.at(i);
            SS now = op(okl,dat.at(l));
            if(!f(now)){
                while(l < siz){
                    l <<= 1;
                    now = op(okl,dat.at(l));
                    if(f(now)){okl = now; l++;}
                }
                return l-siz;
            } 
            okl = now;
        }
        return n;
    }
    int minleft(const function<bool(SS)> f,int r = -1){
        if(r == -1) r = n;
        int l = siz; r += siz;
        vector<int> ls,rs;
        while(l < r){
            if(l&1) ls.push_back(l++);
            if(r&1) rs.push_back(--r);
            l >>= 1; r >>= 1; 
        }
        SS okr = e();
        for(int i=0; i<rs.size(); i++){
            r = rs.at(i);
            SS now = op(dat.at(r),okr);
            if(!f(now)){
                while(r < siz){
                    r <<= 1; r++;
                    now = op(dat.at(r),okr);
                    if(f(now)){okr = now; r--;}
                }
                return r+1-siz;
            }
        }
        for(int i=ls.size()-1; i>=0; i--){
            r = ls.at(i);
            SS now = op(dat.at(r),okr);
            if(!f(now)){
                while(r < siz){
                    r <<= 1; r++;
                    now = op(dat.at(r),okr);
                    if(f(now)){okr = now; r--;}
                }
                return r+1-siz;
            }
        }
        return 0;
    }
    //ノーマルセグ木.一年の時を経て漸く二分探索実装した.
};

int main() {
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);

    int N,K; cin >> N >> K;
    vector<mint> A(N),B(N);
    for(auto &a : A) cin >> a.v;
    for(auto &a : B) cin >> a.v;

    mint sum = 1;
    SegmentTree Z; Z.make2(N,A);
    vector<mint> dp(N+1);
    dp.at(0) = 1;
    for(int i=1; i<=N; i++){
        mint a = A.at(i-1),b = B.at(i-1);
        dp.at(i) = sum*b;
        sum *= a; sum += dp.at(i);
        if(i >= K) sum -= Z.rangeans(i-K,i)*dp.at(i-K);
    }

    sum = 0;    
    vector<mint> dp2(N+1);
    for(int i=K; i<N; i++) dp2.at(i+1) = Z.rangeans(i-K,i)*dp.at(i-K)*B.at(i);
    dp2.at(N) += Z.rangeans(N-K,N)*dp.at(N-K);
    for(int i=1; i<=N; i++){
        mint a = A.at(i-1),b = B.at(i-1);
        dp2.at(i) += sum*b;
        sum *= a; sum += dp2.at(i);
        if(i >= K+1) sum -= Z.rangeans(i-K-1,i)*dp2.at(i-K-1);
    }
    cout << sum.v << endl;
}