One key can only open one lock. If there are 5 keys and 5 locks messed up, the maximum number of times to try to open can determine which key opens which lock.
一把钥匙只能开一把锁，现有5把钥匙和5把锁搞乱了，最多试开多少次就能确定哪把钥匙开哪把锁．
<gadget id="calculator">4 + 3 + 2 + 1</gadget>
<output>10</output>

<result>10</result>