Put 8 balls of each color in a box, and take out at least 4 balls to ensure that you get two balls of the same color.
把多少种颜色的球各8个放在一个盒子里，至少取出4个球，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>