Mix 5 balls of each of the three colors of black, white, and red and put them into a cloth bag. How many balls can be drawn at least each time to ensure that there must be two balls of the same color.
把黑、白、红三种颜色的小球各5个混在一起放入布袋中，每次最少摸出多少个才能保证一定有两个同色的小球．
<gadget id="calculator">3 + 1</gadget>
<output>4</output>

<result>4</result>