Five balls of red, yellow, and blue colors are placed in the same box, and at least how many balls are taken to ensure that two balls of the same color are taken.
有红、黄、蓝三种颜色的球各5个放在同一个箱子里，至少取多少个球，可以保证取到两个颜色相同的球．
<gadget id="calculator">3 + 1</gadget>
<output>4</output>

<result>4</result>