使用Inputbox任意输入三个边长，判断是否能构成三角形，若能构成三角形，则判断该三角形是等边、等腰还是一般三角形。(Inputbox arbitrarily input three sides to judge whether a triangle can be formed. If a triangle can be formed, it is judged to be an equilateral, an isosceles, or a general triangle)