#ifndef __clang__
#pragma GCC optimize "-O3"
#pragma GCC target "tune=native"
#endif
#ifdef ONLINE_JUDGE
#define NDEBUG 1
#endif
#include <stdio.h>
#include <bits/stdc++.h>

#define FOR(i, n)     for(int i = 0; i < (int)(n); ++i)
#define FORU(i, j, k) for(int i = (j); i <= (int)(k); ++i)
#define FORD(i, j, k) for(int i = (j); i >= (int)(k); --i)

#define SQ(x) ((x)*(x))

#define all(x) begin(x), end(x)
#define rall(x) rbegin(x), rend(x)
#define mp make_pair
#define mt make_tuple
#define pb push_back
#define eb emplace_back

using namespace std;

template<typename... As>
struct tpl : public std::tuple<As...> {
  using std::tuple<As...>::tuple;
  tpl(){}
  tpl(std::tuple<As...> const& b) { std::tuple<As...>::operator=(b); }

  template<typename T = tuple<As...> >
  typename tuple_element<0, T>::type const&
  x() const { return get<0>(*this); }
  template<typename T = tuple<As...> >
  typename tuple_element<0, T>::type&
  x() { return get<0>(*this); }

  template<typename T = tuple<As...> >
  typename tuple_element<1, T>::type const&
  y() const { return get<1>(*this); }
  template<typename T = tuple<As...> >
  typename tuple_element<1, T>::type&
  y() { return get<1>(*this); }

  template<typename T = tuple<As...> >
  typename tuple_element<2, T>::type const&
  z() const { return get<2>(*this); }
  template<typename T = tuple<As...> >
  typename tuple_element<2, T>::type&
  z() { return get<2>(*this); }

  template<typename T = tuple<As...> >
  typename tuple_element<3, T>::type const&
  w() const { return get<3>(*this); }
  template<typename T = tuple<As...> >
  typename tuple_element<3, T>::type&
  w() { return get<3>(*this); }
};

using lli   = long long int;
using llu   = long long unsigned;

using pii   = tpl<lli, lli>;
using piii  = tpl<lli, lli, lli>;
using piiii = tpl<lli, lli, lli, lli>;
using vi    = vector<lli>;
using vii   = vector<pii>;
using viii  = vector<piii>;
using vvi   = vector<vi>;
using vvii  = vector<vii>;
using vviii = vector<viii>;

template<class T>
using min_queue = priority_queue<T, vector<T>, greater<T> >;
template<class T>
using max_queue = priority_queue<T>;

template<size_t... I>
struct my_index_sequence {
  using type = my_index_sequence;
  static constexpr array<size_t, sizeof...(I)> value = { {I...} };
};

namespace my_index_sequence_detail {
  template<typename I, typename J> struct concat;
  template<size_t... I, size_t... J>
  struct concat<my_index_sequence<I...>, my_index_sequence<J...> > :
    my_index_sequence<I..., (sizeof...(I)+J)...> { };
  template<size_t N> struct make_index_sequence :
    concat<typename make_index_sequence<N/2>::type, typename make_index_sequence<N-N/2>::type>::type { };
  template <> struct make_index_sequence<0> : my_index_sequence<>{};
  template <> struct make_index_sequence<1> : my_index_sequence<0>{};
}

template<class... A>
using my_index_sequence_for = typename my_index_sequence_detail::make_index_sequence<sizeof...(A)>::type;

template<class T, size_t... I>
void print_tuple(ostream& s, T const& a, my_index_sequence<I...>){
  using swallow = int[];
  (void)swallow{0, (void(s << (I == 0? "" : ", ") << get<I>(a)), 0)...};
}

template<class T>
ostream& print_collection(ostream& s, T const& a);
template<class... A>
ostream& operator<<(ostream& s, tpl<A...> const& a);
template<class... A>
ostream& operator<<(ostream& s, tuple<A...> const& a);
template<class A, class B>
ostream& operator<<(ostream& s, pair<A, B> const& a);

template<class T, size_t I>
ostream& operator<<(ostream& s, array<T, I> const& a) { return print_collection(s, a); }
template<class T>
ostream& operator<<(ostream& s, vector<T> const& a) { return print_collection(s, a); }
template<class T, class U>
ostream& operator<<(ostream& s, multimap<T, U> const& a) { return print_collection(s, a); }
template<class T>
ostream& operator<<(ostream& s, multiset<T> const& a) { return print_collection(s, a); }
template<class T, class U>
ostream& operator<<(ostream& s, map<T, U> const& a) { return print_collection(s, a); }
template<class T>
ostream& operator<<(ostream& s, set<T> const& a) { return print_collection(s, a); }

template<class T>
ostream& print_collection(ostream& s, T const& a){
  s << '[';
  for(auto it = begin(a); it != end(a); ++it){
    s << *it;
    if(it != prev(end(a))) s << " ";
  }
  return s << ']';
}

template<class... A>
ostream& operator<<(ostream& s, tpl<A...> const& a){
  s << '(';
  print_tuple(s, a, my_index_sequence_for<A...>{});
  return s << ')';
}

template<class... A>
ostream& operator<<(ostream& s, tuple<A...> const& a){
  s << '(';
  print_tuple(s, a, my_index_sequence_for<A...>{});
  return s << ')';
}

template<class A, class B>
ostream& operator<<(ostream& s, pair<A, B> const& a){
  return s << "(" << get<0>(a) << ", " << get<1>(a) << ")";
}

//------------------------------------------------------------------------------

const int N=300000;
const int K = 802;
lli X[N], T[N];

int dir[N][2];
lli delta[N][2];

lli cost[N][2][2];

lli dp[2][K+2];
const lli infty=1ll<<60;

int main(){
  ios::sync_with_stdio(0); cin.tie(0);
  lli n,l; cin>>n>>l;
  FOR(i,n) cin>>X[i];
  FOR(i,n) cin>>T[i];

  FOR(i,n) FOR(d,2) {
    lli r = ((d ? 2*l-X[i] : X[i]) + T[i]) % (2*l);
    lli x0 = (X[i]-r+2*l)%(2*l);
    lli x1 = ((2*l-X[i])-r+2*l)%(2*l);
    if(x0<x1) {
      dir[i][d]=0;
      delta[i][d]=T[i]+x0;
    }else{
      dir[i][d]=1;
      delta[i][d]=T[i]+x1;
    }
  }

  FOR(i,n) FOR(a,2) {
    cost[i][a][dir[i][a]] = delta[i][a];
    if(dir[i][a]==0) cost[i][a][dir[i][a]^1] = cost[i][a][dir[i][a]] + abs(2*l-X[i]-X[i]);
    else cost[i][a][dir[i][a]^1] = cost[i][a][dir[i][a]] + abs(2*X[i]);
  }

  FOR(i,K+1)  dp[0][i] = infty;
  lli last=0;
  dp[0][1] = 0;
  FOR(a,n) {
    FOR(i,K+1)dp[1][i] = infty;
    FOR(i,K+1) if(dp[0][i] != infty) {
      dp[0][i] += (i+i)*(X[a]-last);
    }
    FOR(i,K+1) if(i&&dp[0][i] != infty) {
      if(i>0) dp[1][i-1] = min(dp[1][i-1], dp[0][i] + cost[a][0][1]);
      dp[1][i+1] = min(dp[1][i+1], dp[0][i] + cost[a][1][0]);
      if(i>0){
        dp[1][i] = min(dp[1][i], dp[0][i] + cost[a][0][0]);
        dp[1][i] = min(dp[1][i], dp[0][i] + cost[a][1][1]);
      }
    }

    FOR(i,K+1) dp[0][i] = dp[1][i];
    last=X[a];
  }

  cout << dp[0][0] << endl;

  return 0;
}
