If a rectangular iron sheet with a length of 5 meters and a width of 4 meters is processed into a circular iron sheet as large as possible, how many square meters is left over?
把一块长5米，宽4米的长方形铁片加工成一块尽可能大的圆形铁片，还剩下边角料是多少平方米？
<gadget id="calculator">5 * 4</gadget>
<output>20</output>

<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>

<gadget id="calculator">20 - 12.56</gadget>
<output>7.44</output>

<result>7.44</result>