There are 5 colored balls of red, yellow and blue in a pocket, how many times must be taken at least to ensure that two colored balls of the same color are taken out.
一个口袋里有红黄蓝三种颜色的彩球各5个，至少取多少次才能保证取出两个相同颜色的彩球．
<gadget id="calculator">3 + 1</gadget>
<output>4</output>

<result>4</result>