There are 5 red, yellow and blue table tennis balls of the same size in the box. If you want to draw out the balls, there must be 2 of the same color. The minimum number of balls must be drawn out.
盒子里有同样大小的红、黄、蓝3种颜色的乒乓球各5个，要想摸出的球一定有2个同色的，最少要摸出多少个球．
<gadget id="calculator">3 + 1</gadget>
<output>4</output>

<result>4</result>