Symmetric Projections
Description
You are given a set of n points on the plane. A line containing the origin is called good, if projection of the given set to this line forms a symmetric multiset of points. Find the total number of good lines.
Multiset is a set where equal elements are allowed.
Multiset is called symmetric, if there is a point P on the plane such that the multiset is centrally symmetric in respect of point P.
The first line contains a single integer n (1 ≤ n ≤ 2000) — the number of points in the set.
Each of the next n lines contains two integers xi and yi ( - 106 ≤ xi, yi ≤ 106) — the coordinates of the points. It is guaranteed that no two points coincide.
If there are infinitely many good lines, print -1.
Otherwise, print single integer — the number of good lines.
Input
The first line contains a single integer n (1 ≤ n ≤ 2000) — the number of points in the set.
Each of the next n lines contains two integers xi and yi ( - 106 ≤ xi, yi ≤ 106) — the coordinates of the points. It is guaranteed that no two points coincide.
Output
If there are infinitely many good lines, print -1.
Otherwise, print single integer — the number of good lines.
3<br>1 2<br>2 1<br>3 3<br>
2<br>4 3<br>1 2<br>
3<br>
-1<br>
Note
Picture to the first sample test:
In the second sample, any line containing the origin is good.