# Sgu512 Friendly Points

时间限制：5s 空间限制：128MB

### 题目描述

Consider

*n*distinct points on a plane.

Two points from that set are said to be

*friends*, when there exists a rectangle with sides parallel to coordinate axes that contains those two points and doesn't contain any other point from the given set. A rectangle is said to

*contain*a point if the point lies within the rectangle or on its border.

How many pairs of friends are there among the given points?

求这样的点对个数：以两点连线为对角线的矩形内不存在其他点（也不能在边界上）

### 输入格式

The first line of the input file contains an integer

The next

*n*,1<=N<=100 000.The next

*n*lines contain two integers each, the coordinates of the given points. The coordinates don't exceed 10^{9}by absolute value.### 输出格式

Output one integer number — the sought number of pairs of friends.

### 样例输入

5 0 0 0 2 2 0 2 2 1 1

### 样例输出

8

### 提示

没有写明提示

### 题目来源

没有写明来源