There are 3 red balls, 5 yellow balls, and 7 blue balls of the same size and texture in the pocket. If you want to draw out the balls, there must be 2 of the same color. At least how many balls must be drawn out.
口袋里装有同样大小、同样质地的红球3个，黄球5个，蓝球7个，要想摸出的球一定有2个同色的，至少要摸出多少个球．
<gadget id="calculator">3 + 1</gadget>
<output>4</output>

<result>4</result>