#include <bits/stdc++.h>
//#include <atcoder/all>
using namespace std;
//using namespace atcoder;
//using mint = modint1000000007;
//const int mod = 1000000007;
//using mint = modint998244353;
//const int mod = 998244353;
//const int INF = 1e9;
//const long long LINF = 1e18;
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define rep2(i,l,r)for(int i=(l);i<(r);++i)
#define rrep(i, n) for (int i = (n-1); i >= 0; --i)
#define rrep2(i,l,r)for(int i=(r-1);i>=(l);--i)
#define all(x) (x).begin(),(x).end()
#define allR(x) (x).rbegin(),(x).rend()
#define endl "\n"
#define P pair<int,int>
template<typename A, typename B> inline bool chmax(A & a, const B & b) { if (a < b) { a = b; return true; } return false; }
template<typename A, typename B> inline bool chmin(A & a, const B & b) { if (a > b) { a = b; return true; } return false; }

int main() {
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	int n, l; cin >> n >> l;
	set<int>sta, stb;
	rep(i, n) {
		int _; cin >> _;
		sta.insert(_);
	}
	rep(i, n) {
		int _; cin >> _;
		stb.insert(_);
	}
	int pos = *sta.begin();
	sta.erase(pos);
	long long ans = pos;
	rep(i, n - 1) {
		{
			auto itr = stb.upper_bound(pos);
			if (stb.end() == itr) itr = stb.begin();
			int nb = *itr;

			itr = sta.upper_bound(nb);
			if (sta.end() == itr) itr = sta.begin();
			int na = *itr;

			itr = stb.upper_bound(na);
			if (stb.begin() == itr) itr = stb.end();
			itr--;

			int npos = *itr;
			if (npos > pos)ans += npos - pos;
			else ans += l + npos - pos;
			stb.erase(npos);
			pos = npos;
		}
		{
			auto itr = sta.upper_bound(pos);
			if (sta.end() == itr) itr = sta.begin();

			int npos = *itr;

			if (npos > pos)ans += npos - pos;
			else ans += l + npos - pos;
			sta.erase(npos);
			pos = npos;
		}
	}
	auto npos = *stb.begin();
	if (npos > pos)ans += npos - pos;
	else ans += l + npos - pos;

	cout << ans << endl;
	return 0;
}