The keys to 40 locks are messed up. What is the maximum number of attempts to get each lock to have its own key?
40把锁的钥匙搞乱了，为了使每把锁都配上自己的钥匙，至多要试多少次？
<gadget id="calculator">39 + 1</gadget>
<output>40</output>

<gadget id="calculator">39 / 2</gadget>
<output>39/2 = around 19.5</output>

<gadget id="calculator">40 * (39/2)</gadget>
<output>780</output>

<result>780</result>