One key can only open one lock. Now there are 8 locks and 8 keys mixed together. It is hard to tell which key opens which lock. How many times can you try to match these keys and locks one by one? ．
一把钥匙只能开一把锁，现在有8把锁和8把钥匙混在一起，分不清哪把钥匙开哪把锁，最多试验多少次，就能把这些钥匙和锁一一配成对．
<gadget id="calculator">7 + 6 + 5 + 4 + 3 + 2 + 1</gadget>
<output>28</output>

<result>28</result>