Students in a certain class have to vote for class leaders from 8 candidates. If each student can only vote for two candidates, how many students should there be in this class to ensure that there must be three or more students? Vote for the same two candidates.
某班同学要从8名候选人中投票选举班干部，如果每个同学只能投票任选两名候选人，试问这个班至少应有多少名同学，才能保证必定有三个或三个以上的同学投相同两名候选人的票．
<gadget id="calculator">7 + 6 + 5 + 4 + 3 + 2 + 1</gadget>
<output>28</output>

<gadget id="calculator">28 * 2</gadget>
<output>56</output>

<gadget id="calculator">56 + 1</gadget>
<output>57</output>

<result>57</result>