There are 50 people in class 3 and 2, 25 people in the music interest group, 19 people in the sports interest group, and 12 people in both kinds of interest groups. How many people did not participate in either group?
三2班有50人，参加音乐兴趣小组的有25人，参加体育兴趣小组的有19人，其中有12人两种兴趣小组都参加．两种小组都没参加的有多少人？
<gadget id="calculator">19 - 12</gadget>
<output>7</output>

<gadget id="calculator">25 + 7</gadget>
<output>32</output>

<gadget id="calculator">50 - 32</gadget>
<output>18</output>

<result>18</result>