A pocket contains 5 red, yellow and blue colored balls each. At least how many balls are taken out to ensure that there must be two colored balls of the same color among the taken out balls.
一个口袋里有红黄蓝三种颜色的彩球各5个．至少取出多少个球才能保证取出的球中一定有两个颜色相同的彩球．
<gadget id="calculator">3 + 1</gadget>
<output>4</output>

<result>4</result>