There are red, yellow, and green flags, and each person randomly draws 3 flags. To ensure that at least 3 people draw the same flags, how many people must draw the flags?
有红、黄、绿三种颜色小旗若干，每人随意抽取3面小旗，要想保证至少有3人抽取的小旗完全一样的，至少要有多少人来抽取小旗？
<gadget id="calculator">3 * 2</gadget>
<output>6</output>

<gadget id="calculator">3 + 6 + 1</gadget>
<output>10</output>

<gadget id="calculator">10 * 2</gadget>
<output>20</output>

<gadget id="calculator">20 + 1</gadget>
<output>21</output>

<result>21</result>