There are many socks of the same model but different colors in a cardboard box. The colors are red, yellow, black, and white. It is not allowed to see with the eyes, so at least how many socks must be taken to ensure that there are 2 pairs of socks of the same color.
一只纸板箱里装有许多型号相同但颜色不同的袜子，颜色有红、黄、黑、白四种．不允许用眼睛看，那么至少要取多少只袜子，才能保证有2双同色的袜子．
<gadget id="calculator">5 + 1 + 1</gadget>
<output>7</output>

<result>7</result>