There are several chickens and rabbits in the cage, 10 heads are counted from the top, and 36 feet are counted from the bottom. How many chickens are there?
笼子里有鸡兔若干只，从上面数10个头，从下面数36只脚．有多少只鸡．
<gadget id="calculator">10 * 2</gadget>
<output>20</output>

<gadget id="calculator">36 - 20</gadget>
<output>16</output>

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

<gadget id="calculator">16 / 2</gadget>
<output>8</output>

<gadget id="calculator">10 - 8</gadget>
<output>2</output>

<result>2</result>