512. Friendly Points
Time limit per test: 2.5
second(s)
Memory limit: 262144
kilobytes
input: standard
output: standard
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?
Input
The first line of the input file contains an integer
n,
.
The next
n lines contain two integers each, the coordinates of the given points. The coordinates don't exceed 10
^{9} by absolute value.
Output
Output one integer number — the sought number of pairs of friends.
Example(s)
sample input

sample output

5
0 0
0 2
2 0
2 2
1 1

8
