Assemble a circle into an approximate rectangle. It is known that the perimeter of this rectangle is 16.56 decimeters. Find the area of the circle.
将一个圆拼成一个近似的长方形，已知这个长方形的周长是16.56分米，求圆的面积．
<gadget id="calculator">2 ** 2</gadget>
<output>4</output>

<gadget id="calculator">3.14 * 4</gadget>
<output>12.56</output>

<result>12.56</result>