Put 10 balls of each of the four colors red, green, blue, and white into a bag. At least how many balls are taken to ensure that two balls of different colors are taken.
把红、绿、蓝、白四种颜色的球各10个放到一个袋子里．至少取多少个球，可以保证取到两个不同颜色的球．
<gadget id="calculator">10 + 1</gadget>
<output>11</output>

<result>11</result>