Write a program that inputs the lengths of three sides of a shape (positive integers `a`, `b` and `c`, in that order). Three lengths form a valid triangle only if the sum of any two sides is **greater than** the third side. Output one of: - `Not a triangle` - `Equilateral` (all sides equal) - `Isosceles` (exactly two sides equal) - `Scalene` (no sides equal)