How many days does a trade fair last from December 20 to January 28?
某展销会从12月20日到元月28日为期多少天．
<gadget id="calculator">31 - 20</gadget>
<output>11</output>

<gadget id="calculator">11 + 1 + 28</gadget>
<output>40</output>

<result>40</result>