A goat in a kitchen garden

Time Limit: 2.0 second

Memory Limit: 1 000 K

Someone has let a goat in a square kitchen-garden and had bound it to a stake. The stake is driven into the ground in the very midst of the square. The goat is hungry as a hunter and very voracious, and eats everything that can be reached without leaving the square and tearing the roap. What area of the kitchen-garden will be ate round?

1. Input

contains lengths of the garden sides and a cord length in meters (natural numbers not exceeding 100, located in one line and separated with a space).

2. Output

should contain an area of the kitchen-garden (in square meters to within 3 symbols after a decimal point), ate round by the goat.

3. Sample Input

{{{10 6 }}}

4. Sample Output

{{{95.091 }}}

http://acm.timus.ru/problem.aspx?space=1&num=1084