There are 45 students in a class who participate in extracurricular interest groups, among which 34 students participate in the aircraft model group, and 26 students participate in the chess group, and everyone participates in at least one group, how many students participate in both groups in this class.
一个班有45名学生参加课外兴趣小组，其中参加航模小组的有34人，参加象棋小组的有26人，并且每个人都至少参加一个小组，则这个班两个小组都参加的有多少人．
<gadget id="calculator">34 + 26</gadget>
<output>60</output>

<gadget id="calculator">60 - 45</gadget>
<output>15</output>

<result>15</result>