#include <bits/stdc++.h>   #pragma GCC optimize( Ofast )   #pragma GCC target( sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,tune=native )   #pragma GCC optimize( unroll-loops )   using namespace std;   template <typename T1, typename T2>   inline void chkmin(T1 &first, T2 second) {     if (first > second) first = second;   }   template <typename T1, typename T2>   inline void chkmax(T1 &first, T2 second) {     if (first < second) first = second;   }   template <typename T, typename U>   inline ostream &operator<<(ostream &_out, const pair<T, U> &_p) {     _out << _p.first <<     << _p.second;     return _out;   }   template <typename T, typename U>   inline istream &operator>>(istream &_in, pair<T, U> &_p) {     _in >> _p.first >> _p.second;     return _in;   }   template <typename T>   inline ostream &operator<<(ostream &_out, const vector<T> &_v) {     if (_v.empty()) {       return _out;     }     _out << _v.front();     for (auto _it = ++_v.begin(); _it != _v.end(); ++_it) {       _out <<     << *_it;     }     return _out;   }   template <typename T>   inline istream &operator>>(istream &_in, vector<T> &_v) {     for (auto &_i : _v) {       _in >> _i;     }     return _in;   }   template <typename T>   inline ostream &operator<<(ostream &_out, const set<T> &_s) {     if (_s.empty()) {       return _out;     }     _out << *_s.begin();     for (auto _it = ++_s.begin(); _it != _s.end(); ++_it) {       _out <<     << *_it;     }     return _out;   }   template <typename T>   inline ostream &operator<<(ostream &_out, const multiset<T> &_s) {     if (_s.empty()) {       return _out;     }     _out << *_s.begin();     for (auto _it = ++_s.begin(); _it != _s.end(); ++_it) {       _out <<     << *_it;     }     return _out;   }   template <typename T>   inline ostream &operator<<(ostream &_out, const unordered_set<T> &_s) {     if (_s.empty()) {       return _out;     }     _out << *_s.begin();     for (auto _it = ++_s.begin(); _it != _s.end(); ++_it) {       _out <<     << *_it;     }     return _out;   }   template <typename T>   inline ostream &operator<<(ostream &_out, const unordered_multiset<T> &_s) {     if (_s.empty()) {       return _out;     }     _out << *_s.begin();     for (auto _it = ++_s.begin(); _it != _s.end(); ++_it) {       _out <<     << *_it;     }     return _out;   }   template <typename T, typename U>   inline ostream &operator<<(ostream &_out, const map<T, U> &_m) {     if (_m.empty()) {       return _out;     }     _out <<  (  << _m.begin()->first <<  :   << _m.begin()->second <<  ) ;     for (auto _it = ++_m.begin(); _it != _m.end(); ++_it) {       _out <<  , (  << _it->first <<  :   << _it->second <<  ) ;     }     return _out;   }   template <typename T, typename U>   inline ostream &operator<<(ostream &_out, const unordered_map<T, U> &_m) {     if (_m.empty()) {       return _out;     }     _out <<  (  << _m.begin()->first <<  :   << _m.begin()->second <<  ) ;     for (auto _it = ++_m.begin(); _it != _m.end(); ++_it) {       _out <<  , (  << _it->first <<  :   << _it->second <<  ) ;     }     return _out;   }   const int MAXN = 2e5 + 1;   int n;   long long len;   int a[MAXN];   int b[MAXN];   int pref[MAXN * 3];   int v[MAXN];   long long get(int i) {     int d = i / n;     if (i < 0) --d;     return len * d + a[i - d * n];   }   bool check(int d) {     for (int i = 0; i < n * 3; ++i) {       pref[i] = 0;     }     int L = -n, R = 0;     for (int i = 0; i < n; ++i) {       v[i] = 0;       while (abs(get(L) - b[i]) > d) {         if (L > n * 2) return false;         ++L;       }       chkmax(R, L);       while (abs(get(R) - b[i]) <= d) {         ++R;       }       if (R - L >= n) {         pref[0]++;         pref[n]--;       } else {         pref[L + n * 2 - i]++;         pref[R + n * 2 - i]--;       }     }     int b = 0;     for (int i = 0; i < n * 3; ++i) {       b += pref[i];       v[i % n] += b;     }     for (int i = 0; i < n; ++i) {       if (v[i] == n) return true;     }     return false;   }   int main() {     ios::sync_with_stdio(0);     cin >> n >> len;     for (int i = 0; i < n; ++i) {       cin >> a[i];     }     for (int i = 0; i < n; ++i) {       cin >> b[i];     }     sort(a, a + n);     sort(b, b + n);     int L = -1, R = len;     while (R - L > 1) {       int M = (L + R) >> 1;       if (check(M)) {         R = M;       } else {         L = M;       }     }     cout << R << endl;   }