One key can only open one lock. Now there are 5 keys and 5 locks, but I don’t know which key can open which lock. If all the keys match the locks, what is the maximum number of trial openings?
一把钥匙只能开一把锁，现在有5把钥匙5把锁，但不知哪把钥匙开哪把锁，若使全部的钥匙和锁相匹配，试开的次数最多是多少次
<gadget id="calculator">4 + 3 + 2 + 1</gadget>
<output>10</output>

<result>10</result>