# [Usaco2005 dec]Barn Expansion 牛棚扩张

时间限制：5s 空间限制：64MB

### 题目描述

Farmer John has N (1 <= N <= 25,000) rectangular barns on his farm, all with sides parallel to the X and Y axes and integer corner coordinates in the range 0..1,000,000. These barns do not overlap although they may share corners and/or sides with other barns. Since he has extra cows to milk this year, FJ would like to expand some of his barns. A barn has room to expand if it does not share a corner or a wall with any other barn. That is, FJ can expand a barn if all four of its walls can be pushed outward by at least some amount without bumping into another barn. If two barns meet at a corner, neither barn can expand. Please determine how many barns have room to expand.

### 输入格式

* Line 1: A single integer, N

* Lines 2..N+1: Four space-separated integers A, B, C, and D, describing one barn. The lower-left corner of the barn is at (A,B) and the upper right corner is at (C,D).

### 输出格式

* Line 1: A single integer that is the number of barns that can be expanded.

输出可扩张的牛棚数．

### 样例输入

5 0 2 2 7 3 5 5 8 4 2 6 4 6 1 8 6 0 0 8 1 INPUT DETAILS: There are 5 barns. The first barn has its lower-left corner at (0,2) and its upper-right corner at (2,7), and so on.

### 样例输出

2 仅有前两个牛棚可以扩张．

### 提示

没有写明提示

### 题目来源

Gold