keys and 6 locks. If you mess up the keys, how many times can you try to open all the locks?
6把钥匙6把锁，搞乱了钥匙，那么最多试开多少次才能打开所有的锁．
<gadget id="calculator">5 + 4 + 3 + 2 + 1</gadget>
<output>15</output>

<result>15</result>