There are 52 students in a class, including 35, 30 and 20 students who like mathematics, Chinese and English respectively, 22 people, 18 people and 12 people who like two subjects, and 4 people who don't like three subjects. People, how many people are interested in all three subjects?
一个班级有52人，其中爱好数学、语文、英语的各有35人、30人和20人，爱好其中两科的各有22人、18人和12人，三门学科都不爱好的有4人，三门学科都爱好的有多少人？
<gadget id="calculator">20 - 22 - 18 - 12</gadget>
<output>-32</output>

<gadget id="calculator">35 + 30 + (-32)</gadget>
<output>33</output>

<gadget id="calculator">52 - 4 - 33</gadget>
<output>15</output>

<result>15</result>