#include <bits/stdc++.h>

using namespace std;

#define rep(i,n) REP(i,0,n)
#define REP(i,s,e) for(int i=(s); i<(int)(e); i++)
#define repr(i, n) REPR(i, n, 0)
#define REPR(i, s, e) for(int i=(int)(s-1); i>=(int)(e); i--)
#define pb push_back
#define all(r) r.begin(),r.end()
#define rall(r) r.rbegin(),r.rend()
#define fi first
#define se second

typedef long long ll;
typedef vector<int> vi;
typedef vector<ll> vl;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;

const int INF = 1e9;
const ll MOD = 1e9 + 7;
double EPS = 1e-8;

int main() {
    ll N, L;
    cin >> N >> L;
    vector<ll> x(N), y(N);
    rep(i, N) cin >> x[i];
    rep(i, N) cin >> y[i];
    set<ll> X, Y;
    rep(i, N) {
        X.insert(x[i]);
        Y.insert(y[i]);
    }

    auto getIt = [](const set<ll>& st, ll val) {
        auto it = st.upper_bound(val);
        if (it != st.end()) return it;
        return st.begin();
    };

    ll ans = 0LL;
    ll cur = 0LL;

    rep(i, N) {
        {
            auto itX = getIt(X, cur);
            if (cur < *itX) ans += (*itX - cur);
            else ans += (L - cur + *itX);
            cur = *itX;
            X.erase(itX);
        }
        // cout << " " << cur;
        {
            auto itY = getIt(Y, cur);
            // cout << "(first itY " << *itY << "), ";
            if(X.size() > 0) {
                auto itX = getIt(X, *itY);
                // cout << " (nxt itX " << *itX << "), "; 
                {
                    itY = getIt(Y, *itX);
                    // cout << "(nxt itY " << *itY << "), ";
                    if(itY == Y.begin()) {
                        itY = Y.end();
                    }
                    --itY;
                }
            }
            if (cur < *itY) ans += (*itY - cur);
            else ans += (L - cur + *itY);
            cur = *itY;
            Y.erase(itY);
        }
        // cout << " " << cur << " -> " << ans << endl;
    }

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