There are 20 rows of seats in a lecture theater, the first row has 10 seats, and each subsequent row has one more seat than the previous row. If candidates in each row are not allowed to sit next to each other during the exam, then the lecture theater can at most How many candidates are sitting.
某个阶梯教室，有20排座位，第一排有10个座位，以后每一排比前一排多一个座位，如果考试时每一排的考生都不许相邻而坐，那么这阶梯教室最多能坐多少个考生．
<gadget id="calculator">10 + 28</gadget>
<output>38</output>

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

<gadget id="calculator">38 * (5/2)</gadget>
<output>95</output>

<gadget id="calculator">11 + 29</gadget>
<output>40</output>

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

<gadget id="calculator">40 * 5</gadget>
<output>200</output>

<gadget id="calculator">200 + 10</gadget>
<output>210</output>

<gadget id="calculator">210 / 2</gadget>
<output>105</output>

<gadget id="calculator">95 + 105</gadget>
<output>200</output>

<result>200</result>