There are 9 keys and 9 locks, one key can only open one of the locks, but we don't know which key will open which lock, and how many times will it take to match all the keys and locks.
有9把钥匙9把锁，一把钥匙只能打开其中的一把锁，但不知道哪把钥匙开哪把锁，最多要试多少次才能配好所有的钥匙和锁．
<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>