Tudor has decided to build a triangular pen for his goats!
Tudor has identified locations on his farm where he can install fence posts. To construct a pen, Tudor will install fence posts at exactly three locations, and then build fences between those fence posts.
For obvious reasons, Tudor must select fence posts such that there is strictly positive area for the goats to roam around inside.
How many different pens can Tudor construct? Two pens are different if a fence post is installed in one but not in the other.
In tests worth 5 marks,
All fence post candidate locations will be pairwise distinct.
The first line of the input is a single positive integer .
lines follow, each containing two space-separated integers and , indicating that a fence post can be installed at .
Output, on a single line, the number of distinct triangular pens Tudor can build.
4 0 0 1 0 2 0 1 1