There are 12 red, yellow, blue, and white balls of the same size in the box. To ensure that 4 balls of the same color are drawn, at least how many balls must be drawn.
盒子里有同样大小的红、黄、蓝、白四种颜色的球各12个，要想保证摸出4个同颜色的球，至少要摸出多少个球．
<gadget id="calculator">4 * 3</gadget>
<output>12</output>

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

<result>13</result>