few good friends go to A, B, C three attractions to play, each only visit two of them, no matter how they arrange the tour plan, at least 4 of them will visit the same attractions. May I ask how many people are at least going to play?
几个要好的朋友去A，B，C三个景点游玩，每人只游览其中的两个景点，不管他们怎样安排游览方案，都至少有4个人游览的景点完全相同．请问至少有几个人去游玩？
<gadget id="calculator">4 - 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>