There is a wall in your backyard. It is so long that you can’t see its endpoints. You want to build a fence of length L such that the area enclosed between the wall and the fence is maximized. The fence can be of arbitrary shape, but only its two endpoints may touch the wall.

given : the length of the fence.

the wanted solution : the largest area. Your answer should be rounded to 2 digits after the decimal point.

eg :

1 -> 0.16

hints : take pi as 3.14159265358.

i want help to find the formula to answer this