There are 10 red, yellow, blue, and white balls in each color, mix them in a cassette, and at least how many balls are drawn at a time can ensure that there are 6 balls of the same color.
有红、黄、蓝、白四色小球各10个，混合放在一个暗盒中，一次至少摸出多少个，才能保证有6个小球是同色的．
<gadget id="calculator">5 * 4</gadget>
<output>20</output>

<gadget id="calculator">20 + 1</gadget>
<output>21</output>

<result>21</result>