cloth bag contains some identical balls except for different colors, among which there are 9 red balls, 6 yellow balls, 2 green balls, and 1 purple ball. Then at least how many balls must be taken from the bag to ensure that 4 balls have the same color.
一个布袋中有一些除颜色不同外其它完全一样的小球，其中红色球有9个，黄色球有6个，绿色球有2个，紫色球有1个．那么至少要从袋子中取出多少个球，才能保证有4个球的颜色相同．
<gadget id="calculator">3 + 3 + 1 + 2 + 1</gadget>
<output>10</output>

<result>10</result>