A bag contains 10 balls of four colors, red, yellow, blue, and green. At least how many balls are taken out of the bag can ensure that there are 2 balls of the same color.
一个袋子里装有红、黄、蓝、绿四种颜色的球各10个，从中至少取出多少个能保证有2个球颜色相同．
<gadget id="calculator">4 * 1</gadget>
<output>4</output>

<gadget id="calculator">4 + 1</gadget>
<output>5</output>

<result>5</result>