Primary school starts summer vacation on July 1st and attends school on August 31st. How many days are there in summer vacation?
小学7月1日暑假开始，8月31日到校上课，暑假共有多少天．
<gadget id="calculator">31 - 1</gadget>
<output>30</output>

<gadget id="calculator">31 + 30</gadget>
<output>61</output>

<result>61</result>