There are several chickens and rabbits in the cage. There are 8 heads counted from the top and 28 feet counted from the bottom. How many chickens are there?
笼子里有若干只鸡和兔，从上面数有8个头，从下面数有28这脚，则鸡有多少只．
<gadget id="calculator">2 * 8</gadget>
<output>16</output>

<gadget id="calculator">28 - 16</gadget>
<output>12</output>

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

<gadget id="calculator">12 / 2</gadget>
<output>6</output>

<gadget id="calculator">8 - 6</gadget>
<output>2</output>

<result>2</result>