There are 72 people in the chorus team organized by the three classes of the fourth grade, 23 people participated in the first class, 28 people participated in the second class, how many people participated in the third class?
四年级三个班组织合唱队共72人，一班参加了23人，二班参加了28人，三班参加了多少人？
<gadget id="calculator">72 - 23 - 28</gadget>
<output>21</output>

<result>21</result>