To cut 5 round iron sheets with a radius of 2 cm, at least a rectangular iron sheet with an area of cm**2 must be prepared.
要剪5个半径为2cm的圆铁片，至少要准备面积是多少cm**2的长方形铁皮．
<gadget id="calculator">2 * 2 * 5</gadget>
<output>20</output>

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

<gadget id="calculator">20 * 4</gadget>
<output>80</output>

<result>80</result>