There are 10 keys and 10 locks, but if you mix up the keys and locks, how many times can you try to find the corresponding keys and locks?
10把钥匙10把锁，但弄乱了钥匙和锁，最多试多少次，才能全部找对相应的钥匙和锁．
<gadget id="calculator">9 + 8 + 7 + 6 + 5 + 4 + 3 + 2 + 1</gadget>
<output>45</output>

<result>45</result>