Wet Shark and Bishops

题意翻译

有一个$1000\times1000$的棋盘，上面有$n(1\le n\le 200000)$个象，每个象的位置为$(x_i,y_i)$。满足$1\le x_i,y_i\le 1000$。 注意，这里的规定与国际象棋的不同。我们认为，只要两个象在同一对角线，就能够相互攻击到（中间有象也没有关系）。 求互相攻击的象的对数。

题目描述

Today, Wet Shark is given $ n $ bishops on a $ 1000 $ by $ 1000 $ grid. Both rows and columns of the grid are numbered from $ 1 $ to $ 1000 $ . Rows are numbered from top to bottom, while columns are numbered from left to right. Wet Shark thinks that two bishops attack each other if they share the same diagonal. Note, that this is the only criteria, so two bishops may attack each other (according to Wet Shark) even if there is another bishop located between them. Now Wet Shark wants to count the number of pairs of bishops that attack each other.

输入输出格式

输入格式

The first line of the input contains $ n $ ( $ 1<=n<=200000 $ ) — the number of bishops. Each of next $ n $ lines contains two space separated integers $ x_{i} $ and $ y_{i} $ ( $ 1<=x_{i},y_{i}<=1000 $ ) — the number of row and the number of column where $ i $ -th bishop is positioned. It's guaranteed that no two bishops share the same position.

输出格式

Output one integer — the number of pairs of bishops which attack each other.

输入输出样例

输入样例 #1

5
1 1
1 5
3 3
5 1
5 5

输出样例 #1

6

输入样例 #2

3
1 1
2 3
3 5

输出样例 #2

0

说明

In the first sample following pairs of bishops attack each other: $ (1,3) $ , $ (1,5) $ , $ (2,3) $ , $ (2,4) $ , $ (3,4) $ and $ (3,5) $ . Pairs $ (1,2) $ , $ (1,4) $ , $ (2,5) $ and $ (4,5) $ do not attack each other because they do not share the same diagonal.