Xiaohong and Xiaojun have a total of 30 serials, Xiaohong has 4 more copies than Xiaojun, how many copies does Xiaojun have.
小红和小军共有连环30本，小红比小军多4本，小军有多少本．
<gadget id="calculator">30 - 4</gadget>
<output>26</output>

<gadget id="calculator">26 / 2</gadget>
<output>13</output>

<result>13</result>