One 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. Now all 4 locks are locked, and they can be opened as many times as possible.
一只钥匙只开一把锁，现有4只钥匙，4把锁，但不知哪把钥匙开哪把锁，现在4只锁全锁着，最多试多少次就可以都打开．
<gadget id="calculator">4 + 3 + 2 + 1</gadget>
<output>10</output>

<result>10</result>