Put 5 balls of red, yellow, and blue colors into a bag, how many balls can be taken at least to ensure that two balls of the same color are taken? Please briefly explain why.
把红、黄、蓝三种颜色的球各5个放到一个袋子里，至少取多少个球可以保证取到两个颜色相同的球？请简要说明理由．
<gadget id="calculator">3 + 1</gadget>
<output>4</output>

<result>4</result>