The school starts summer vacation on July 20th and starts school on September 1st. How many days are there in summer vacation?
学校从7月20号开始放暑假，9月1号上学，暑假一共有多少天．
<gadget id="calculator">31 - 20</gadget>
<output>11</output>

<gadget id="calculator">11 + 1 + 31</gadget>
<output>43</output>

<result>43</result>