There are 20 rows of seats in the examination room, the first row has 20 seats, and each subsequent row has one more seat than the previous row. If candidates are allowed to sit freely, but not next to other candidates, what is the maximum number of candidates that can be accommodated in the examination room?
考试的考场有20排座位，第一排有20个座位，以后各排都比前一排多一个座位．如果允许考生任意坐，但不能坐在其他考生的旁边，该考场最多可容纳多少个考生．
<gadget id="calculator">20 + 38</gadget>
<output>58</output>

<gadget id="calculator">10 / 2 / 2</gadget>
<output>5/2 = around 2.5</output>

<gadget id="calculator">58 * (5/2)</gadget>
<output>145</output>

<gadget id="calculator">21 + 39</gadget>
<output>60</output>

<gadget id="calculator">10 / 2</gadget>
<output>5</output>

<gadget id="calculator">60 * 5</gadget>
<output>300</output>

<gadget id="calculator">300 + 10</gadget>
<output>310</output>

<gadget id="calculator">310 / 2</gadget>
<output>155</output>

<gadget id="calculator">145 + 155</gadget>
<output>300</output>

<result>300</result>