#include <bits/stdc++.h>
using namespace std;
#define F first
#define S second
#define R cin>>
#define Z class
#define ll long long
#define ln cout<<'\n'
#define in(a) insert(a)
#define pb(a) push_back(a)
#define pd(a) printf("%.10f\n",a)
#define mem(a) memset(a,0,sizeof(a))
#define all(c) (c).begin(),(c).end()
#define iter(c) __typeof((c).begin())
#define rrep(i,n) for(ll i=(ll)(n)-1;i>=0;i--)
#define REP(i,m,n) for(ll i=(ll)(m);i<(ll)(n);i++)
#define rep(i,n) REP(i,0,n)
#define tr(it,c) for(iter(c) it=(c).begin();it!=(c).end();it++)
template<Z A>void pr(A a){cout<<a;ln;}
template<Z A,Z B>void pr(A a,B b){cout<<a<<' ';pr(b);}
template<Z A,Z B,Z C>void pr(A a,B b,C c){cout<<a<<' ';pr(b,c);}
template<Z A,Z B,Z C,Z D>void pr(A a,B b,C c,D d){cout<<a<<' ';pr(b,c,d);}
template<Z A>void PR(A a,ll n){rep(i,n){if(i)cout<<' ';cout<<a[i];}ln;}
ll check(ll n,ll m,ll x,ll y){return x>=0&&x<n&&y>=0&&y<m;}
const ll MAX=1e9+7,MAXL=1LL<<61,dx[4]={-1,0,1,0},dy[4]={0,1,0,-1};
typedef pair<ll,ll> P;

void Main() {
  ll n,m;
  cin >> n >> m;
  vector<ll> a(n),b(n);
  rep(i,n) R a[i];
  rep(i,n) R b[i];
  rep(k,2)rep(i,n) a.pb(a[i]+m*(k+1));
  rep(k,2)rep(i,n) b.pb(b[i]+m*(k+1));
  b.pb(-1);
  sort(all(b));
  a.pb(MAXL);
  b.pb(MAXL);
  ll x=-1,ans=0;
  while(n--) {
    ll k1=lower_bound(all(b),x)-b.begin();
    ll y1=b[k1];
    if(y1!=-1) rep(k,3) b.erase(lower_bound(all(b),y1%m+m*k));
    ll k2=lower_bound(all(a),y1)-a.begin();
    ll y2=a[k2];
    ll k3=lower_bound(all(b),y2)-b.begin();
    ll k4=lower_bound(all(a),b[k3])-a.begin();
    ll k5=lower_bound(all(b),a[k4])-b.begin();
    if(x==-1) x=0;
    rep(k,3) a.erase(lower_bound(all(a),y2%m+m*k));
    ans+=abs(x-b[k5-1]);
    x=b[k5-1]%m;
  }
  pr(ans);
}

int main(){ios::sync_with_stdio(0);cin.tie(0);Main();return 0;}