Put 10 table tennis balls of each of the four colors of red, yellow, blue, and green in a box. At least how many table tennis balls must be touched to ensure that there must be 4 table tennis balls of the same color.
把红、黄、蓝、绿四种颜色的乒乓球各10个放在一个箱子里，至少要摸多少个才能保证一定有4个是同色的乒乓球．
<gadget id="calculator">3 * 4</gadget>
<output>12</output>

<gadget id="calculator">12 + 1</gadget>
<output>13</output>

<result>13</result>