There are a number of students who participate in 5 interest groups, and each student participates in exactly 2 groups, and each of the 2 groups has exactly one person the same, how many students participate in these 5 interest groups?
有若干同学参加5个兴趣小组，其中每个同学都恰好参加了2个小组，且每2个小组都恰好有一人相同，则参加这5个兴趣小组的同学共有多少人．
<gadget id="calculator">1 + 2 + 3 + 4</gadget>
<output>10</output>

<result>10</result>