#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;
typedef long long ll;
typedef pair<ll,int> P;
ll N,L,X[100010],Y[100010];
int use[100010] = {};
vector<P> v;

ll del(ll x,ll y){
	if(x<y) return y-x;
	else return L-x+y;
}

int main(){
	cin >> N >> L;
	for(int i=1;i<=N;i++){
		cin >> X[i];
	}
	for(int i=1;i<=N;i++){
		cin >> Y[i];
	}
	for(int i=1;i<=N;i++){
		v.push_back(P(X[i],1));
		v.push_back(P(Y[i],-1));
	}
	sort(v.begin(),v.end());
	ll ans = 0,now_d = 0;
	int cnt = 0,now = 0;
	bool sushi = false;
	while(cnt<2*N){
		if(!sushi){
			for(int j=0;j<=4*N;j++){
				if(use[(now+j)%(2*N)]==1) continue;
				if(v[(now+j)%(2*N)].second==1){
					sushi = true;
					ans += del(now_d,v[(now+j)%(2*N)].first);
					now_d = v[(now+j)%(2*N)].first;
					use[(now+j)%(2*N)] = 1;
					now = (now+j)%(2*N);
					break;
				}
			}
		}else{
			int ocha_id = -1;
			for(int j=0;j<=4*N;j++){
				if(use[(now+j)%(2*N)]==1) continue;
				if(ocha_id!=-1 && v[(now+j)%(2*N)].second==1){
					ans += del(now_d,v[ocha_id].first);
					now_d = v[ocha_id].first;
					now = ocha_id;
					use[ocha_id] = 1;
					sushi = false;
					break;
				}
				if(v[(now+j)%(2*N)].second==-1){
					ocha_id = (now+j)%(2*N);
					if(cnt==2*N-1){
						ans += del(now_d,v[ocha_id].first);
						now_d = v[ocha_id].first;
						now = ocha_id;
						use[ocha_id] = 1;
						sushi = false;
						break;
					}
				}
			}
		}
		cnt++;
	}
	cout << ans << endl;
}