There are 10 small balls in each of the four colors of red, yellow, blue, and white, and they are mixed and put into a cloth bag. How many balls must be drawn at least once to ensure that two balls are of the same color?
有红、黄、蓝、白四种颜色的小球各10个，混合后放到一个布袋里．问一次至少摸出多少个，才能保证有两个球是同色球？
<gadget id="calculator">4 + 1</gadget>
<output>5</output>

<result>5</result>