Put 3 balls of each of the four colors A, B, C, and D in the same box, and at least how many balls must be taken out of the box at a time to ensure that two balls of the same color are taken.
把A、B、C、D四种颜色的球各3个，放在同一个盒子里，一次至少要从盒子里取出多少个球才可以保证取到两个颜色相同的．
<gadget id="calculator">4 + 1</gadget>
<output>5</output>

<result>5</result>