There are several chickens and rabbits in a cage. Counting from the top, there are 13 heads, and counting from the bottom, there are 38 feet. How many chickens are there?
笼子里有若干只鸡和兔．从上面数，有13个头，从下面数，有38只脚．鸡有多少只？
<gadget id="calculator">2 * 13</gadget>
<output>26</output>

<gadget id="calculator">38 - 26</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">13 - 6</gadget>
<output>7</output>

<result>7</result>