CF165A.Supercentral Point

普及/提高-

通过率：0%

AC君温馨提醒

该题目为【codeforces】题库的题目，您提交的代码将被提交至codeforces进行远程评测，并由ACGO抓取测评结果后进行展示。由于远程测评的测评机由其他平台提供，我们无法保证该服务的稳定性，若提交后无反应，请等待一段时间后再进行重试。

题目描述

One day Vasya painted a Cartesian coordinate system on a piece of paper and marked some set of points $(x_{1},y_{1}),(x_{2},y_{2}),...,(x_{n},y_{n})$ . Let's define neighbors for some fixed point from the given set $(x,y)$ :

point $(x',y')$ is $(x,y)$ 's right neighbor, if x'>x and $y'=y$
point $(x',y')$ is $(x,y)$ 's left neighbor, if x'<x and $y'=y$
point $(x',y')$ is $(x,y)$ 's lower neighbor, if $x'=x$ and y'<y
point $(x',y')$ is $(x,y)$ 's upper neighbor, if $x'=x$ and y'>y

We'll consider point $(x,y)$ from the given set supercentral, if it has at least one upper, at least one lower, at least one left and at least one right neighbor among this set's points.

Vasya marked quite many points on the paper. Analyzing the picture manually is rather a challenge, so Vasya asked you to help him. Your task is to find the number of supercentral points in the given set.

输入格式

The first input line contains the only integer $n$ ( $1<=n<=200$ ) — the number of points in the given set. Next $n$ lines contain the coordinates of the points written as " $x$ $y$ " (without the quotes) ( $|x|,|y|<=1000$ ), all coordinates are integers. The numbers in the line are separated by exactly one space. It is guaranteed that all points are different.

输出格式

Print the only number — the number of supercentral points of the given set.

输入输出样例

输入#1
```
8
1 1
4 2
3 1
1 2
0 2
0 1
1 0
1 3
```
输出#1
```
2
```
输入#2
```
5
0 0
0 1
1 0
0 -1
-1 0
```
输出#2
```
1
```

说明/提示

In the first sample the supercentral points are only points $(1,1)$ and $(1,2)$ .

In the second sample there is one supercental point — point $(0,0)$ .

首页