Maximal Area Quadrilateral

###### 题意简述 给定n个点，要求从这些点里面寻找4个点，使得这四个点组成的四边形的面积最大。保证不出现三点共线或点重合的情况 。 感谢 @ REDDEVILS 提供的翻译

Iahub has drawn a set of $ n $ points in the cartesian plane which he calls "special points". A quadrilateral is a simple polygon without self-intersections with four sides (also called edges) and four vertices (also called corners). Please note that a quadrilateral doesn't have to be convex. A special quadrilateral is one which has all four vertices in the set of special points. Given the set of special points, please calculate the maximal area of a special quadrilateral.

The first line contains integer $ n $ ( $ 4<=n<=300 $ ). Each of the next $ n $ lines contains two integers: $ x_{i} $ , $ y_{i} $ $ (-1000<=x_{i},y_{i}<=1000) $ — the cartesian coordinates of $ i $ th special point. It is guaranteed that no three points are on the same line. It is guaranteed that no two points coincide.

Output a single real number — the maximal area of a special quadrilateral. The answer will be considered correct if its absolute or relative error does't exceed $ 10^{-9} $ .

5
0 0
0 4
4 0
4 4
2 3

16.000000

In the test example we can choose first $ 4 $ points to be the vertices of the quadrilateral. They form a square by side $ 4 $ , so the area is $ 4·4=16 $ .