EOJ-自适应编程学习平台

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?

There are several test cases.Each 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).

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