Xiaojun measured the circumference of a tree trunk to be 12.56 cm, and measured the area of the cross-section of the tree trunk in square decimeters.
小军测得一棵树干的周长是12.56厘米，测这树树干的横截面的面积是多少平方分米．
<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>