A key can only open one lock. Now there are 4 keys and 4 locks, but I don't know which key will open which lock. How many times will I have to try to match all the keys and 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，最多要试多少次才能配好全部的钥匙和锁．
<gadget id="calculator">3 + 2 + 1</gadget>
<output>6</output>

<result>6</result>