#include <bits/stdc++.h>
using namespace std;
#define FOR(i,m,n) for(int i=(m);i<(n);++i)
#define REP(i,n) FOR(i,0,n)
using ll = long long;
constexpr int INF = 0x3f3f3f3f;
constexpr long long LINF = 0x3f3f3f3f3f3f3f3fLL;
constexpr double EPS = 1e-8;
constexpr int MOD = 998244353;
// constexpr int MOD = 1000000007;
constexpr int DY4[]{1, 0, -1, 0}, DX4[]{0, -1, 0, 1};
constexpr int DY8[]{1, 1, 0, -1, -1, -1, 0, 1};
constexpr int DX8[]{0, -1, -1, -1, 0, 1, 1, 1};
template <typename T, typename U>
inline bool chmax(T& a, U b) { return a < b ? (a = b, true) : false; }
template <typename T, typename U>
inline bool chmin(T& a, U b) { return a > b ? (a = b, true) : false; }
struct IOSetup {
  IOSetup() {
    std::cin.tie(nullptr);
    std::ios_base::sync_with_stdio(false);
    std::cout << fixed << setprecision(20);
  }
} iosetup;

int main() {
  int n, m; cin >> n >> m;
  vector<int> a(n);
  for (int& a_i : a) cin >> a_i;
  REP(i, n) {
    int b; cin >> b;
    a[i] = (a[i] - b + m) % m;
  }
  vector<int> d(n + 1, a.front());
  FOR(i, 1, n) d[i] = (a[i] - a[i - 1] + m) % m;
  d.back() = (m - a.back()) % m;
  ranges::sort(d, greater<int>());
  const int c = reduce(d.begin(), d.end(), 0LL) / m;
  REP(i, c) d[i] -= m;
  ll ans = 0;
  for (const int& d_i : d) ans += abs(d_i);
  cout << ans / 2 << '\n';
  return 0;
}