static void Main(string[] args) { var courseService = new CourseService(); Console.Write("How many students for course A? "); var quantity = int.Parse(Console.ReadLine()); var A = courseService.AddStudents(quantity); Console.Write("How many students for course B? "); quantity = int.Parse(Console.ReadLine()); var B = courseService.AddStudents(quantity); Console.Write("How many students for course C? "); quantity = int.Parse(Console.ReadLine()); var C = courseService.AddStudents(quantity); var D = new SortedSet <int>(); D.UnionWith(A); D.UnionWith(B); D.UnionWith(C); Console.Clear(); courseService.Print("A", A); courseService.Print("B", B); courseService.Print("C", C); Console.WriteLine(); Console.WriteLine("Total Students: " + D.Count); }