If a key can only open one lock, there are 5 keys and 5 locks, but I don’t know which key can open which lock. How many times should I try to match all the keys and locks?
若一把钥匙能且只能开一把锁，现有5把钥匙5把锁，但不知哪把钥匙开哪把锁，要配好全部钥匙和锁最多要试多少次．
<gadget id="calculator">4 + 3 + 2 + 1</gadget>
<output>10</output>

<result>10</result>