Cut out the largest circle from a rectangle whose length is 8 decimeters and width is 4 decimeters. What is the area of this circle?
在一个长是8分米，宽是4分米的长方形里剪去一个最大的圆，这个圆的面积是多少？
<gadget id="calculator">4 / 2</gadget>
<output>2</output>

<gadget id="calculator">2 ** 2</gadget>
<output>4</output>

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

<result>12.56</result>