I had some trouble passing Test #8.

It turned out that if I used Epsilon = 1e-8 to compare the angles, it worked.

Also, here is a tricky test, with lots of points on the same line:

Input:
10
0 0
1 1
2 2
3 3
4 4
-1 -1
-2 -2
-3 -3
-4 -4
0 1

One possible solution:
10
1
2
3
4
5
10
6
7
8
9