The school will be on holiday from July 15th to September 1st. How many days will the holiday be?
学校从7月15日放假，到9月1日开学，假期多少天．
<gadget id="calculator">31 - 15</gadget>
<output>16</output>

<gadget id="calculator">16 + 1</gadget>
<output>17</output>

<gadget id="calculator">17 + 31</gadget>
<output>48</output>

<result>48</result>