Five small balls of red, yellow, and blue colors are placed in the same box (the balls are the same except for the color), and at least how many balls are taken can ensure that two balls of the same color are taken.
有红黄蓝三种颜色的小球各5个放入同一个箱子内(小球除颜色外其余均相同)，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>