Lan Lan went to the summer camp on July 15th and came back on August 9th. How many days did Lan Lan attend the summer camp?
兰兰从7月15日去参加夏令营，到8月9日回来，兰兰参加的夏令营共有多少天？
<gadget id="calculator">31 - 15</gadget>
<output>16</output>

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

<gadget id="calculator">17 + 9</gadget>
<output>26</output>

<result>26</result>