#include <bits/stdc++.h>
using namespace std;
#pragma region macros_and_aliases
#define rep(i, n) for(long long i = 0; i < (n); i++)
#define rrep(i, n) for(long long i = (n)-1; i > -1; i--)
#define Rep(i, m, n) for(long long i = (m); i < (n); i++)
#define rRep(i, m, n) for(long long i = (n)-1; i >= (m); i--)
#define REP(i, m, n, p) for(long long i = m; i < n; i += p)
#define foa(s, v) for(auto &s : v)
#define all(v) (v).begin(), (v).end()
#define rall(v) (v).rbegin(), (v).rend()
#define pq priority_queue
#define bcnt(n) __builtin_popcountll(n)
#define endk endl
#define ednl endl
#define enld endl
using ll = long long;
using ld = long double;
using vll = vector<ll>;
using vvll = vector<vll>;
using vvvll = vector<vvll>;
using vb = vector<bool>;
using mll = map<long long, long long>;
using pll = pair<long long, long long>;
using qll = queue<long long>;
using sll = set<long long>;
using vpll = vector<pair<long long, long long>>;
template <class T = ll>
using V = vector<T>;
template <class T = ll>
using VV = V<V<T>>;
template <class T = ll>
using VVV = V<V<V<T>>>;
//昇順pq(小さい方から取り出す)
template <class T = ll>
using pqup = priority_queue<T, vector<T>, greater<T>>;
//降順pq(大きい方から取り出す)
template <class T = ll>
using pqdn = priority_queue<T>;
#define debug(var)              \
	std::cout << #var << " : "; \
	view(var)
template <typename T>
void view(T e) {
	std::cout << e << std::endl;
}
template <typename T>
void view(const std::vector<T> &v) {
	for(const auto &e : v) {
		std::cout << e << " ";
	}
	std::cout << std::endl;
}
template <typename T>
void view(const std::vector<std::vector<T>> &vv) {
	for(const auto &v : vv) {
		view(v);
	}
}
template <typename T1, typename T2>
ostream &operator<<(ostream &os, const pair<T1, T2> &p) {
	os << p.first << " " << p.second;
	return os;
}
template <typename T1, typename T2>
istream &operator>>(istream &is, pair<T1, T2> &p) {
	is >> p.first >> p.second;
	return is;
}
#pragma endregion
#pragma region constants

long long const limLL = 9223372036854775807;  // POW(2,63)-1 ~ 9.22e18
long long const dekai = 3e16;
const long double pi = acos(-1);
int dx[4] = {1, 0, -1, 0};
int dy[4] = {0, 1, 0, -1};
int ddx[8] = {-1, -1, -1, 0, 0, 1, 1, 1};
int ddy[8] = {-1, 0, 1, -1, 1, -1, 0, 1};

const int mod = 1000000007;
// const int mod = 998244353;
#pragma endregion
#pragma region vector
//ベクトルの出力(検証済)
// vectorの中身を出力する 答えの出力に利用可能
vector<long long> vin(long long n) {  //整数n個の入力を受け取ってベクトルに突っ込んで返す
	vector<long long> v(n);
	for(long long i = 0; i < n; i++) {
		cin >> v[i];
	}
	return v;
}
template <class T>
void vout(vector<T> &v, bool tate = 0) {
	if(v.size() > 0) {
		for(auto it = v.begin(); it < v.end(); it++) {
			cout << *it;
			if(it != v.end() - 1) {
				if(tate)
					cout << endl;
				else
					cout << " ";
			}
		}
	}
	cout << endl;
}
// vectorの中身を数える map<要素,個数>を返す
template <class T>
map<T, long long> countv(vector<T> v) {
	map<T, long long> m;
	for(auto &g : v) {
		if(m.count(g))
			m[g]++;
		else
			m[g] = 1;
	}
	return m;
}
template <class T>
void add(vector<T> &v, T val) {	 //ベクトルの各要素に加算
	for(auto &a : v) a += val;
	return;
}
#pragma endregion
#pragma region basic_procedure

template <class T>
inline bool isin(T x, T lef, T rig) {
	return ((lef <= x) && (x < rig));
}
template <class T>
inline bool isin(T x, T y, T lef, T rig) {
	return isin(x, lef, rig) && isin(y, lef, rig);
}
template <class T>
inline bool isin(T X, T lefX, T rigX, T Y, T lefY, T rigY) {
	return isin(X, lefX, rigX) && isin(Y, lefY, rigY);
}

template <class T>
inline bool chmin(T &a, T b) {
	if(a > b) {
		a = b;
		return true;
	}
	return false;
}
template <class T>
inline bool chmax(T &a, T b) {
	if(a < b) {
		a = b;
		return true;
	}
	return false;
}

void Yes(bool f = 1) { cout << (f ? "Yes" : "No") << "\n"; }
void No() { cout << "No\n"; }
void YES(bool f = 1) { cout << (f ? "YES" : "NO") << "\n"; }
void NO() { cout << "NO\n"; }
void err() { cout << -1 << endl; }

#pragma endregion

int main() {
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	// cout << fixed << setprecision(15);


	int n;
	cin >> n;

	vector<vector<int>> vec(1001, vector<int>(1001));

	rep(i, n) {
		int x, y, z, w;
		cin >> x >> y >> z >> w;
		vec[x][y]++;
		vec[z][w]++;
		vec[x][w]--;
		vec[z][y]--;
	}

	rep(i, 1001) {
		rep(j, 1000) { vec[i][j + 1] += vec[i][j]; }
	}
	rep(i, 1000) {
		rep(j, 1001) { vec[i + 1][j] += vec[i][j]; }
	}

	int ans = 0;
	rep(i, 1000) rep(j, 1000) chmax(ans, vec[i][j]);
	cout << ans << "\n";
}


Measured memory_bytes: 6864