Randomly dye the small squares in a 5*5 rectangle with black and white colors, and verify: there must be a rectangle composed of several small squares in this rectangle, and the small squares on its four corners Same color.
用黑、白两种颜色将一个5*5的长方形中的小方格随意染色，求证：在这个长方形中一定存在一个由若干小方格组成的长方形，它的四个角上的小方格同色．
<result>4</result>