There are several consecutive odd numbers starting from 1 on the blackboard: 1, 3, 5, 7, 9, 11, 13... If the sum of these odd numbers is 400, what is the last odd number?
黑板上有从1开始的若干个连续的奇数：1、3、5、7、9、11、13…，如果这些奇数之和是400，那么最后一个奇数是多少．
<gadget id="calculator">2 * 20</gadget>
<output>40</output>

<gadget id="calculator">40 - 1</gadget>
<output>39</output>

<result>39</result>