Enclose It

Given lengths of four line segments, you should tell the maximum area they could enclose.

An area is enclosed means it is isolated from the outer part by the four line segments.

Input

There are several test cases. Each case contains four integers in a line, each of which representing the length of a line segment. All integers are in the range of (0, 100).

Proceed to the end of file.

Output

For each test case, output the maximum area the lines could enclose, accurate up to 2 decimal places.

Sample Input

5 5 5 5

Sample Output

25.00