There are 9 keys and 9 locks, one key can open one lock, but I don't know which one to open which one, and how many times at least can all be opened.
有9把钥匙9把锁，一把钥匙开一把锁，但不知道哪把开哪把，最少多少次能够确保全打开．
<gadget id="calculator">8 + 1</gadget>
<output>9</output>

<gadget id="calculator">7 + 2</gadget>
<output>9</output>

<gadget id="calculator">6 + 3</gadget>
<output>9</output>

<gadget id="calculator">5 + 4</gadget>
<output>9</output>

<gadget id="calculator">9 + 9 + 9 + 9</gadget>
<output>36</output>

<result>36</result>