There are 5 balls in each of the five colors of red, yellow, blue, green, and white. How many balls are taken at least to ensure that there are two balls of the same color?
有红、黄、蓝、绿、白五种颜色的球各5个，至少取多少个球，可以保证有两个颜色相同的球？
<gadget id="calculator">5 + 1</gadget>
<output>6</output>

<result>6</result>