QUADAREA  Maximal Quadrilateral Area
You are trying to build a house, but unfortunately you currently have only four available walls with side lengths a, b, c, and d. You want your house to be as big as possible, so you would like to know the largest possible area of any quadrilateral you can construct with these four side lengths.
Input
The first line contains the integer T (1 ≤ T ≤ 2,000), the number of tests. Each test contains a single line with four real numbers: a, b, c, and d (0 < a, b, c, d < 1,000). Note that it will always be possible to form a valid quadrilateral with these lengths; that is, the sum of any three side lengths will be strictly larger than the other one.
Output
For each test case, print a single line containing the largest possible area. Your output will be accepted if it is within 0.01 of the official answer.
Example
Input: 2 1 2 1 2 0.5 0.5 0.5 0.5 Output: 2.00 0.25
For the first test case, it is optimal to construct a rectangle, and for the second, a square is optimal.
hide comments
Rudradeep Mukherjee:
20130713 14:55:14
No need to push for more precision. :) 

Aayush Gupta:
20130711 12:51:40
use double!! 

Sivaraman Nagarajan:
20130225 03:58:30
For the first test case, it is optimal to construct a rectangle, and for the second, a square is optimal. Why is this statement 

Ouditchya Sinha:
20130202 08:15:35
Easy question... My 50th AC :) 

Paul Draper:
20121211 08:15:55
@Saransh Bansal, I feel you. I had TLE with java.util.Scanner. After I made my own I/O functions, I have #2 Java solution. 

Avinash Mishra:
20120731 06:59:07
cout<<ans<<endl not working getting WA but printf("%lf\n",ans)working why? 

npsabari:
20120618 08:53:10
@The Champ: Thanks, float gave WA and double worked. 

MR. BEAN :
20120618 07:31:26
my 850th submission and 200th accepted problem :)


Vrian7:
20120602 01:23:38
Problem Easy.... 
Added by:  Neal Wu 
Date:  20080524 
Time limit:  1s 
Source limit:  50000B 
Memory limit:  1536MB 
Cluster:  Cube (Intel G860) 
Languages:  All except: ERL JSRHINO 