There are 36 students in a class who participate in music, art, and sports interest groups. Each student participates in at least one group, and at most two groups. It is known that the number of people participating in music, art, and sports interest groups are 26, 15, and 13 respectively. There are 6 people who participate in music and art, and 4 people who participate in art and sports at the same time, how many people participate in music and sports at the same time
某班有36名同学参加音乐、美术、体育兴趣小组，每名同学至少参加一个小组，最多参加两个小组，已知参加音乐、美术、体育兴趣小组的人数分别为26，15，13，同时参加音乐和美术的有6人，同时参加美术和体育的有4人，则同时参加音乐和体育的人数为多少
<gadget id="calculator">13 - 6 - 4 - 36</gadget>
<output>-33</output>

<gadget id="calculator">26 + 15 + (-33)</gadget>
<output>8</output>

<result>8</result>