The school stipulates that each student should participate in at least one of the Chinese interest group and the mathematics interest group. There are 45 students in Class 204, 30 people in the Chinese interest group, 22 people in the mathematics interest group, and both Chinese and mathematics interest groups. how many people.
学校规定每个学生至少参加语文兴趣小组和数学兴趣小组中的一个，204班有45人，参加语文兴趣小组的有30人，参加数学兴趣小组的有22人，语文和数学兴趣小组都参加的有多少人．
<gadget id="calculator">22 - 45</gadget>
<output>-23</output>

<gadget id="calculator">30 + (-23)</gadget>
<output>7</output>

<result>7</result>