There are enough red and white balls in the pocket, and several people take turns to take the balls from the pocket, and each person takes 3 balls. To ensure that the balls taken by 4 people are of the same color, at least how many people should take the balls.
口袋里放有足够多的红、白两种颜色的球，由若干个人轮流从袋中取球，每人取3个．若要保证有4人取出的球的颜色完全相同，至少应有多少人取球．
<gadget id="calculator">4 - 1</gadget>
<output>3</output>

<gadget id="calculator">4 * 3</gadget>
<output>12</output>

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

<result>13</result>