Xiao Ming is the 7th from the left in the morning exercise team, the 13th from the right, the 8th from the front, and the 14th from the back. The number of people in each row is the same. How many students do the exercises?
小明在早操队伍中左起第7个，右起第13个，从前边数第8个，后边数第14个，每行人数一样多，做操的同学共有多少人？
<gadget id="calculator">13 - 1</gadget>
<output>12</output>

<gadget id="calculator">7 + 12</gadget>
<output>19</output>

<gadget id="calculator">14 - 1</gadget>
<output>13</output>

<gadget id="calculator">8 + 13</gadget>
<output>21</output>

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

<result>399</result>