There are several balls of 5 colors in the carton, how many balls should be taken from them at least to ensure that four balls of the same color are taken?
纸盒里有5种颜色的小球若干个，从中至少取多少个才能保证取到四个颜色相同的？
<gadget id="calculator">3 * 5</gadget>
<output>15</output>

<gadget id="calculator">15 + 1</gadget>
<output>16</output>

<result>16</result>