The school holiday starts on July 15th and starts on August 31st. How many days are there in total?
学校7月15日开始放假，8月31日开学，共放假多少天．
<gadget id="calculator">31 - 15</gadget>
<output>16</output>

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

<gadget id="calculator">17 + 30</gadget>
<output>47</output>

<result>47</result>