Li Huan measured the circumference of the trunk of a tree with a ruler to be 12.56dm, so how many square decimeters is the cross-sectional area of the trunk of this tree?
李欢用尺量得一棵树的树干的周长是12.56dm，则这棵树的树干横截面的面积有多少平方分米？
<gadget id="calculator">2 * 3.14</gadget>
<output>6.28</output>

<gadget id="calculator">12.56 / 6.28</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>