Vote for three singers A, B, and C. Each voter can vote for any two singers. At least how many people vote to ensure that at least 4 of them vote exactly the same.
给甲、乙、丙三位歌手投票，每位投票人可投给任意两名歌手，至少有多少个人投票，才能保证其中至少有4个投票人的投票情况完全相同．
<gadget id="calculator">2 + 1</gadget>
<output>3</output>

<gadget id="calculator">3 * 3</gadget>
<output>9</output>

<gadget id="calculator">9 + 1</gadget>
<output>10</output>

<result>10</result>