There are 5 locks and 5 keys that match each other, but now the locks and keys are messed up. The lock and the key can be paired with each other in as many trials as possible.
有5把锁和5把钥匙是互相配对的，但现在锁和钥匙弄乱了．最多需要试多少次，就可以将锁和钥匙互相配对．
<gadget id="calculator">4 + 3 + 2 + 1</gadget>
<output>10</output>

<result>10</result>