#include "bits/stdc++.h"
using namespace std;
typedef long long ll;
typedef pair<int,int> pii;
typedef pair<ll,ll> pll;
const int INT = 1e9;
const ll LINF = 1e17;

void solve(){
    int N; cin >> N;
    vector<vector<int>> imos(1010,vector<int>(1010,0));
    for(int i = 0; i < N;i++){
        int x1,y1,x2,y2; cin >> x1 >> y1 >> x2 >> y2;
        x1++;y1++;x2++;y2++;
        imos[x1][y1]++;
        imos[x1][y2]--;
        imos[x2][y1]--;
        imos[x2][y2]++;
    }
    int ans = 0;
    for(int i = 1; i< 1010;i++){
        for(int j = 1; j< 1010;j++){
            imos[i][j] += (imos[i-1][j]+imos[i][j-1]-imos[i-1][j-1]);
            ans = max(ans,imos[i][j]);
        }
    }
    cout << ans << endl;
}
int main(void){
    cin.tie(0); ios_base::sync_with_stdio(false);
    solve();
    return 0;
}
