Our school starts winter vacation on January 18th, and registration starts on February 15th. How many days are there in this holiday?
我们学校从1月18日开始放寒假，2月15日开学报名，这个假期共有多少天．
<gadget id="calculator">31 - 18</gadget>
<output>13</output>

<gadget id="calculator">15 - 1</gadget>
<output>14</output>

<gadget id="calculator">13 + 1 + 14</gadget>
<output>28</output>

<result>28</result>