1 pen can be exchanged for 3 ballpoint pens, 1 ballpoint pen can be exchanged for 4 pencils, and how many pencils can 1 pen be exchanged for.
1支钢笔可以换3支圆珠笔，1支圆珠笔可以换4支铅笔，1支钢笔可以换多少支铅笔．
<gadget id="calculator">4 * 3</gadget>
<output>12</output>

<result>12</result>