There are 10 red, yellow and blue balls with exactly the same shape in the bag. Each child can only touch one ball out of the bag. Only by how many children touch the ball can there be two touches. The balls are the same color.
袋中有外形完全一样的红、黄、蓝三种颜色的小球各10个，每个小朋友只能从中摸出1个小球，至少有多少个小朋友摸球，才能保证一定有两个人摸的球颜色一样．
<gadget id="calculator">3 + 1</gadget>
<output>4</output>

<result>4</result>