#include <bits/stdc++.h>
using namespace std;

#define sz(x) (int)(x).size()
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
#define pb push_back
#define x first
#define y second
#define FOR(i, a, b) for(int i = (a); i < (b); i++)
#define RFOR(i, a, b) for(int i = (a) - 1; i >= (b); i--)

typedef long long ll;
typedef double db;
typedef long double LD;
typedef pair<int, int> pii;
typedef pair<db, db> pdd;
typedef pair<ll, ll> pll;

struct SegTree
{
	int n;
	vector<ll> cnt, sm;
	vector<ll> am;
	
	SegTree(int _n, const vector<ll>& _am)
	{
		n = _n;
		cnt.assign(4 * n, 0);
		sm.assign(4 * n, 0);
		am = _am;
	}
	
	void update(int v, int st, int en, int l, int r, int del)
	{
		if (st > r || en < l)
			return;
		
		if (st >= l && en <= r)
		{
			cnt[v] += del;
		}
		else
		{
			int mid = (st + en) / 2;
			update(2 * v, st, mid, l, r, del);
			update(2 * v + 1, mid + 1, en, l, r, del);
		}
		
		if (cnt[v] > 0)
		{
			sm[v] = am[en + 1] - am[st];
		}
		else if (st == en)
		{
			sm[v] = 0;
		}
		else
		{
			sm[v] = sm[2 * v] + sm[2 * v + 1];
		}
	}
	ll query()
	{
		return sm[1];
	}
};

struct Event
{
	ll x, y1, y2;
	int del;
	
	Event(ll _x, ll _y1, ll _y2, int _del) : x(_x), y1(_y1), y2(_y2), del(_del) {} 
	
	bool operator<(const Event& oth)
	{
		if (this->x == oth.x)
		{
			return this->del > oth.del;
		}
		return this->x < oth.x;
	}
};

int solve()
{
	int n;
	if (!(cin >> n))
		return 1;
	
	vector<Event> a;
	set<ll> ys;
	FOR (i, 0, n)
	{
		ll x1, y1, x2, y2;
		cin >> x1 >> y1 >> x2 >> y2;
		a.pb(Event(x1, y1, y2, 1));
		a.pb(Event(x2, y1, y2, -1));
		ys.insert(y1);
		ys.insert(y2);
	}
	sort(all(a));
	
	int j = 0;
	map<ll, int> m;
	for (ll el: ys)
		m[el] = j++;
	
	FOR (i, 0, sz(a))
	{
		a[i].y1 = m[a[i].y1];
		a[i].y2 = m[a[i].y2];
	}
	
	vector<ll> am;
	for (auto [key, val]: m)
		am.pb(key);
	
	int nn = sz(ys);
	SegTree st(nn, am);
	ll ans = 0;
	ll prX = a[0].x;
	FOR (i, 0, sz(a))
	{
		ll x = a[i].x, y1 = a[i].y1, y2 = a[i].y2;
		int del = a[i].del;
		ans += (x - prX) * st.query();
		st.update(1, 0, nn - 1, y1, y2 - 1, del);
		prX = x;
	}
	cout << ans << '\n';
	
	return 0;
}

int32_t main()
{
	ios::sync_with_stdio(0);
	cin.tie(0);
	
	int TET = 1e9;
	//cin >> TET;
	for (int i = 1; i <= TET; i++)
	{
		if (solve())
		{
			break;
		}
		#ifdef ONPC
			cerr << "_____________________________\n";
		#endif
	}
	#ifdef ONPC
		cerr << "\nfinished in " << clock() * 1.0 / CLOCKS_PER_SEC << " sec\n";
	#endif
	return 0;
}