#include using namespace std; using int64 = long long; const int mod = 1e9 + 7; const int inf = (1 << 30) - 1; const int64 infll = (1LL << 61) - 1; struct IoSetup { IoSetup() { cin.tie(nullptr); ios::sync_with_stdio(false); cout << fixed << setprecision(10); cerr << fixed << setprecision(10); } } iosetup; template< typename T > ostream &operator<<(ostream &os, const vector< T > &v) { for(int i = 0; i < (int) v.size(); i++) { os << v[i] << (i + 1 != v.size() ? " " : ""); } return os; } template< typename T > istream &operator>>(istream &is, vector< T > &v) { for(T &in : v) is >> in; return is; } template< typename T1, typename T2 > inline bool chmax(T1 &a, T2 b) { return a < b && (a = b, true); } template< typename T1, typename T2 > inline bool chmin(T1 &a, T2 b) { return a > b && (a = b, true); } template< typename T = int64 > vector< T > make_v(size_t a) { return vector< T >(a); } template< typename T, typename... Ts > auto make_v(size_t a, Ts... ts) { return vector< decltype(make_v< T >(ts...)) >(a, make_v< T >(ts...)); } template< typename T, typename V > typename enable_if< is_class< T >::value == 0 >::type fill_v(T &t, const V &v) { t = v; } template< typename T, typename V > typename enable_if< is_class< T >::value != 0 >::type fill_v(T &t, const V &v) { for(auto &e : t) fill_v(e, v); } template< typename T > struct edge { int src, to; T cost; edge(int to, T cost) : src(-1), to(to), cost(cost) {} edge(int src, int to, T cost) : src(src), to(to), cost(cost) {} edge &operator=(const int &x) { to = x; return *this; } operator int() const { return to; } }; template< typename T > using Edges = vector< edge< T > >; template< typename T > using WeightedGraph = vector< Edges< T > >; using UnWeightedGraph = vector< vector< int > >; template< typename T > using Matrix = vector< vector< T > >; int main() { int N, L; cin >> N >> L; vector< pair< int, int > > mp; for(int z = 0; z < 2; z++) { for(int i = 0; i < N; i++) { int p; cin >> p; mp.emplace_back(p, z); } } sort(begin(mp), end(mp)); auto check = [&](int sz) { vector< int > st[2]; for(auto &p : mp) { if(p.second == 0) { if(st[1].empty()) { if(st[0].size() + st[1].size() <= sz) { st[p.second].emplace_back(p.first); continue; } return make_pair(false, -1); } st[1].pop_back(); st[0].emplace_back(p.first); } else { if(st[0].empty()) { if(st[0].size() + st[1].size() <= sz) { st[p.second].emplace_back(p.first); continue; } return make_pair(false, -1); } st[0].pop_back(); st[1].emplace_back(p.first); } } if(st[1].empty()) return make_pair(true, 0); return make_pair(true, st[1][0]); }; int ok = N, ng = -1; while(ok - ng > 1) { int mid = (ok + ng) / 2; if(check(mid).first) ok = mid; else ng = mid; } cout << 1LL * ok * L + check(ok).second << endl; }