Maximum area of quadrilateral

Given four sides of quadrilateral a, b, c, d, find the maximum area of the quadrilateral possible from the given sides .
Examples: 

Input : 1 2 1 2
Output : 2.00
It is optimal to construct a rectangle for maximum area .

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According to Bretschneider's formula, the area of a general quadrilateral is given by 
Here a, b, c, d are the sides of a quadrilateral, s is the semiperimeter of a quadrilateral and angles are two opposite angles. 
So, this formula is maximized only when opposite angles sum to pi(180) then we can use a simplified form of Bretschneider's formula to get the (maximum) area K. 

This formula is called as Brahmagupta's formula . 
Below is the implementation of given approach

Output: 

2.00

Time Complexity: O(logn) 
Auxiliary Space: O(1)

Please suggest if someone has a better solution which is more efficient in terms of space and time.