2 sheep weigh the same as 1 pig, 4 pigs weigh the same as 1 cow, and 2 cows weigh the same as how many sheep.
2只羊和1头猪同样重，4头猪和1头牛同样重，2头牛和多少只羊同样重．
<gadget id="calculator">4 * 2 * 2</gadget>
<output>16</output>

<result>16</result>