The sum of two consecutive odd numbers is 40, what is the product of these two odd numbers?
两个连续奇数的和是40，这两个奇数的积是多少．
<gadget id="calculator">40 / 2</gadget>
<output>20</output>

<gadget id="calculator">20 - 1</gadget>
<output>19</output>

<gadget id="calculator">20 + 1</gadget>
<output>21</output>

<gadget id="calculator">19 * 21</gadget>
<output>399</output>

<result>399</result>