Problem I. 9. Area
Input file name: standard input
Output file name: standard output
Time limit: 1 s
Memory limit: 1024 MB
Output file name: standard output
Time limit: 1 s
Memory limit: 1024 MB
Three squares with side lengths A, B, and C are placed side by side in decreasing order, as shown below: 
Calculate the area of the shaded region.
Input
Three integers A, B, C (1 \le C < B < A \le 100).
Output
Print the area of the shaded region with two digits after the decimal point.
Example
| standard input | standard output |
|---|---|
| 9 6 4 | 47.50 |