#include <bits/stdc++.h>
using namespace std;
const int INF = 1e9 + 7;
const long long INFL = 1e18 + 123;
const double PI = atan2(0, -1);
mt19937 tw(960172);
long long rnd(long long x, long long y) {
  static uniform_int_distribution<long long> d;
  return d(tw) % (y - x + 1) + x;
}
int cur_sum, deleted_sum;
vector<tuple<int, int, int>> back, front;
void init() {
  cur_sum = 0;
  deleted_sum = 0;
  back.clear();
  front.clear();
}
int get_min_back() {
  if (((int)(back).size())) {
    return get<2>(back.back());
  }
  return INF;
}
int get_min_front() {
  if (((int)(front).size())) {
    return get<2>(front.back());
  }
  return INF;
}
void add(int val) {
  cur_sum += val;
  back.push_back({val, cur_sum, min(cur_sum, get_min_back())});
}
void pop() {
  assert(((int)(back).size()) || ((int)(front).size()));
  if (!((int)(front).size())) {
    while (((int)(back).size())) {
      int val, sum, tmp;
      tie(val, sum, tmp) = back.back();
      back.pop_back();
      front.push_back({val, sum, min(sum, get_min_front())});
    }
  }
  deleted_sum += get<0>(front.back());
  front.pop_back();
}
int get_min() { return min(get_min_front(), get_min_back()) - deleted_sum; }
void solve() {
  int n, l;
  cin >> n >> l;
  vector<int> boys, girls;
  for (int i = 0; i < n; ++i) {
    int num;
    cin >> num;
    boys.push_back(num);
    boys.push_back(num + l);
  }
  for (int i = 0; i < n; ++i) {
    int num;
    cin >> num;
    girls.push_back(num - l);
    girls.push_back(num);
    girls.push_back(num + l);
  }
  sort(boys.begin(), boys.end());
  sort(girls.begin(), girls.end());
  int lg = -1, rg = l / 2;
  while (rg - lg > 1) {
    int mid = (lg + rg) / 2;
    init();
    bool flag = true;
    int c1 = 0, c2 = 0, c3 = 0;
    while (girls[c2] - mid <= boys[c1]) {
      ++c2;
    }
    c3 = c2;
    while (c3) {
      if (boys[0] - girls[c3 - 1] <= mid) {
        --c3;
      } else {
        break;
      }
    }
    int c0 = c2;
    for (int i = 0; i < n; ++i) {
      while (girls[c3] < boys[i] - mid) {
        ++c3;
      }
      while (girls[c0] - mid <= boys[i]) {
        ++c0;
      }
      c2 = max(c2, c0);
      while (true) {
        if (girls[c2] - mid <= boys[c1]) {
          if (c2 == c3 + n) {
            break;
          }
          add(1);
          ++c2;
        } else {
          if (boys[c1] + mid >= boys[i] + l - mid) {
            break;
          }
          add(-1);
          ++c1;
        }
      }
      if (c0 - c3 + get_min() < 0) {
        flag = false;
        break;
      }
      if (i == n - 1) {
        break;
      }
      int tmp = deleted_sum;
      pop();
      --tmp;
      assert(tmp == deleted_sum);
      while ((((int)(front).size()) || ((int)(back).size())) &&
             girls[c0] - mid <= boys[i + 1]) {
        pop();
        ++tmp;
        ++c0;
      }
      assert(tmp == deleted_sum);
    }
    if (flag) {
      rg = mid;
    } else {
      lg = mid;
    }
  }
  cout << rg << "\n";
}
int main() {
  cerr << fixed << setprecision(15);
  cout << fixed << setprecision(15);
  ios::sync_with_stdio(false);
  int tests = 1;
  for (int it = 1; it <= tests; ++it) {
    solve();
  }
  return 0;
}
