Problem C - Convex ordering
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You are given the vertices of a convex polygon (mathematically a polygon
is convex if a line joining any two vertices is on or inside the
polygon) in some order. Your task is to order the vertices in a
counterclockwise manner, starting from the rightmost vertex.  For
simplicity, you may assume that the x-coordinates of all points are
distinct. 

Input
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The input will contain multiple instances. Each instance has two lines.
The first line contains a single integer, which is the number of points
n (0 < n < 10000). The second line contains 2n floating point numbers
(separated by a single blank space), x1,y1,x2,y2,....,xn,yn. The end of
the input will be indicated by a line containing 0. This case chould not
be processed.

Output
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The output should contain one line for each case. Each line should have
2n floating point numbers (separated by a single blank space),
x1,y1,x2,y2,....,xn,yn. 

Sample input
------------

4
-1 0 1 0 0.001 1 0 -1
0

Sample output
-------------

1 0 0.001 1 -1 0 0 -1