area of shaded region

[goofyjud]

I have a box with a circle inside, the edge of the circle touches the sides of the square box. the sides of the square is 2 the area that is shaded are the 4 corners. What is the area of the shaded region?

 

[Denis]

area of the shaded region = area of square - area of circle

radius of circle = 1 : understand ?