A key can only open one lock. Now there are 4 keys and 4 locks, but I don’t know which key can open which lock. How many times can I open all the locks?
一把钥匙只能开一把锁，现在有4把钥匙4把锁，但不知哪把钥匙开哪把锁，问最多试多少次可以打开所有的锁．
<gadget id="calculator">3 + 2 + 1</gadget>
<output>6</output>

<result>6</result>