The students are doing radio gymnastics. There are 15 rows in total. There are 4 people in the first row. After that, each row has one more person than the previous row. How many students do the exercises?
同学们做广播体操，一共排了15排，第一排4人，以后每排比前一排多1人，共有多少学生做操？
<gadget id="calculator">15 - 1</gadget>
<output>14</output>

<gadget id="calculator">14 * 1</gadget>
<output>14</output>

<gadget id="calculator">4 + 4 + 14</gadget>
<output>22</output>

<gadget id="calculator">15 / 2</gadget>
<output>15/2 = around 7.5</output>

<gadget id="calculator">22 * (15/2)</gadget>
<output>165</output>

<result>165</result>