#include <bits/stdc++.h>
using namespace std;
#if __has_include("all.hpp")
#include "all.hpp"
#else
#include <atcoder/all>
#endif
using namespace atcoder;
using mint=modint998244353;
int main(void){
    int n,k;
    cin>>n>>k;
    vector<long long>a(n),b(n);
    for(int i=0;i<n;i++)cin>>a[i];
    for(int i=0;i<n;i++)cin>>b[i];
    mint suma=0,sumb=0,r=0;
    for(int i=0;i<n;i++){
        suma+=a[i];
        sumb+=b[i];
        r+=a[i]*b[i];
    }
    cout<<((suma*sumb-r)*(n/k-1)/(n-1)).val()<<endl;
    return 0;
}