pocket contains 10 black balls, 7 white balls and 4 red balls. At least how many balls can be drawn to ensure that there are 2 balls of the same color.
一个口袋中有10个黑球，7个白球和4个红球．至少摸出多少个球就能保证有2个球颜色相同．
<gadget id="calculator">3 + 1</gadget>
<output>4</output>

<result>4</result>