There are 5 pairs of sports shoes of the same specification in four colors of red, blue, yellow and black, and they are stacked in a big cloth bag in a messy manner. If you take the shoes with your eyes closed, at least how many shoes are taken out of the bag. In order to ensure that there are 2 pairs of sports shoes of the same color.
有红、蓝、黄、黑四种颜色同一规格的运动鞋各5双，杂乱地堆放在一个大布袋中．如果闭着眼睛取鞋，至少从袋中取出多少只鞋．才能保证有2双同色的运动鞋．
<gadget id="calculator">4 * 5</gadget>
<output>20</output>

<gadget id="calculator">20 + 4 + 1</gadget>
<output>25</output>

<result>25</result>