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

int a[10001][10001];

signed main(){

  int n; cin >> n;
  for(int i = 0; i < n; i++){
    int x1,y1,x2,y2;
    cin >> x1 >> y1 >> x2 >> y2;
    a[y1][x1]++;
    a[y2][x1]--;
    a[y1][x2]--;
    a[y2][x2]++;
  }

  int ans = 0;
  for(int i = 0; i < 1000; i++){
    for(int j = 0; j < 1000; j++){
      if(i) a[i][j] += a[i-1][j];
      if(j) a[i][j] += a[i][j-1];
      if(i && j) a[i][j] -= a[i-1][j-1];
      ans = max(ans,a[i][j]);
    }
  }
  cout << ans << endl;

  return 0;
}

