There are 10 red, yellow and blue glass balls of the same size in each of the three colors, put them into a box, and at least how many glass balls are drawn out can guarantee to get two balls of the same color.
有相同大小的红、黄、蓝三种颜色的玻璃球各10个，放入一个盒子里，至少摸出多少个个，就可以保证取到两个颜色相同的球．
<gadget id="calculator">3 + 1</gadget>
<output>4</output>

<result>4</result>