A rectangular plank with a length of 5dm and a width of 4dm is sawn into a largest circular plank, what is the area of the circular plank in dm**2.
把一块长5dm，宽4dm的长方形木板锯成一个最大的圆形木板，这个圆形木板的面积是多少dm**2．
<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>