Kata

A circle of radius r is divided into n equal sectors(shaped like pieces of pie). Each sector has two sides that are each a radius of the circle. Next, turn each sector into a triangle by placing a line(chord) between the points where the radii of the sector intersects with the circle. Return the total area of n triangles rounded to 10 decimal places.

Input:

Number of triangles n.

Radius of circle r.

Output:

Sum of area of n triangles rounded to 10 decimal places.

Conditions:

Both n and r are positive integers.

n >= 3

1 <= r <= 10

Default value for radius r is 1.