<image>As shown in the image, we know that to prevent a quadrilateral wooden frame from deforming, at least one wooden strip must be nailed. So, how many wooden strips are needed at minimum to prevent a pentagonal wooden frame from deforming? How many wooden strips are needed at minimum to prevent a heptagonal wooden frame from deforming? How many wooden strips are needed at minimum to prevent an n-sided polygonal wooden frame from deforming?