One key can only open one lock. Now there are 8 keys and 8 locks that are all messed up. How many trials will it take to match all the locks and corresponding keys?
一把钥匙只能开一把锁，现在有8把钥匙和8把锁全部都搞乱了，最多要试验多少次才能全部配好锁和相应的钥匙．
<gadget id="calculator">7 + 6 + 5 + 4 + 3 + 2 + 1</gadget>
<output>28</output>

<result>28</result>