A1335.[COCI-2007_2008-contest3]#3 DEJAVU

N points are placed in the coordinate plane.
Write a program that calculates how many ways we can choose three points so that they form a right triangle with legs parallel to the coordinate axes.
A right triangle has one 90-degree internal angle. The legs of a right triangle are its two shorter sides.

The first line of input contains the integer N (3 ≤ N ≤ 100000), the number of points.
Each of the following N lines contains two integers X and Y (1 ≤ X, Y ≤ 100 000), the coordinates of one point.
No pair of points will share the same pair of coordinates.

Output the number of triangles.

In 40% of all test cases, N will be less than 100.
In 70% of all test cases, N will be less than 10000.