#include <bits/stdc++.h>
using namespace std;
typedef signed long long ll;

#define _P(...) (void)printf(__VA_ARGS__)
#define FOR(x,to) for(x=0;x<(to);x++)
#define FORR(x,arr) for(auto& x:arr)
#define FORR2(x,y,arr) for(auto& [x,y]:arr)
#define ALL(a) (a.begin()),(a.end())
#define ZERO(a) memset(a,0,sizeof(a))
#define MINUS(a) memset(a,0xff,sizeof(a))
template<class T> bool chmax(T &a, const T &b) { if(a<b){a=b;return 1;}return 0;}
template<class T> bool chmin(T &a, const T &b) { if(a>b){a=b;return 1;}return 0;}
//-------------------------------------------------------

int N,K;
int A[202020];
int B[202020];
ll SA,SB;
const ll mo=998244353;

ll modpow(ll a, ll n = mo-2) {
	ll r=1;a%=mo;
	while(n) r=r*((n%2)?a:1)%mo,a=a*a%mo,n>>=1;
	return r;
}

ll fact[202020];


void solve() {
	int i,j,k,l,r,x,y; string s;
	
	cin>>N>>K;
	FOR(i,N) {
		cin>>A[i];
		SA+=A[i];
	}
	FOR(i,N) {
		cin>>B[i];
		SB+=B[i];
	}
	ll ret=(SA%mo)*(SB%mo)%mo;
	FOR(i,N) ret+=mo-1LL*A[i]*B[i]%mo;
	
	ret=ret*(N/K-1)%mo*modpow(N-1)%mo;
	
	fact[0]=1;
	FOR(i,N) fact[i+1]=fact[i]*(i+1)%mo;
	ret=ret*fact[N]%mo;
	FOR(i,K) ret=ret*modpow(fact[N/K])%mo;
	ret=ret*modpow(fact[K])%mo;
	
	cout<<ret<<endl;
	
}


int main(int argc,char** argv){
	string s;int i;
	if(argc==1) ios::sync_with_stdio(false), cin.tie(0);
	FOR(i,argc-1) s+=argv[i+1],s+='\n'; FOR(i,s.size()) ungetc(s[s.size()-1-i],stdin);
	cout.tie(0); solve(); return 0;
}