There are 10 red balls, 10 yellow balls, and 10 blue balls in a bag. How many balls must be taken out to ensure that there are two pairs of balls of the same color?
一个袋子里有红，黄，蓝各10个小球，至少要拿出多少个球，才能保证有两对同色球？
<gadget id="calculator">3 * 3</gadget>
<output>9</output>

<gadget id="calculator">9 + 1</gadget>
<output>10</output>

<result>10</result>