Put 5 balls of each color into a bag, and take at least 4 balls to ensure that you get two balls of the same color.
将多少种颜色的球各5个放到一个袋里，至少取4个，可以保证取到两个颜色相同的球．
<gadget id="calculator">4 - 1</gadget>
<output>3</output>

<result>3</result>