static void Main()
        {
            Students[] students = new Students[3];
            students[0] = new Students("Boyko", "Borisov", 20);
            students[1] = new Students("Sashka", "Vaseva", 60);
            students[2] = new Students();

            Console.WriteLine("Task 3");
            foreach (var student in FirstNameBeforeLast(students))
                Console.WriteLine(student);

            Console.WriteLine();
            Console.WriteLine("Task 4");

            foreach (var student in FindStudentFrom18To24(students))
                Console.WriteLine(student);

            Console.WriteLine();
            Console.WriteLine("Task 5");

            Students[] studentsByLambda = students.OrderByDescending(x => x.FirstName).ThenByDescending(x => x.LastName).ToArray();
            Students[] studentsByLINQ = OrderStudentsLINQ(students);
            foreach (var student in studentsByLINQ)
                Console.WriteLine(student);
        }
 //Task 5
 public static Students[] OrderStudentsLINQ(Students[] listOfStudents)
 {
     var ordered = from student in listOfStudents
                   orderby student.FirstName descending, student.LastName descending
                   select student;
     return ordered.ToArray();
 }
 // Task 3
 public static Students[] FirstNameBeforeLast(Students[] listOfStudents)
 {
     return listOfStudents.Where(x => x.FirstName.CompareTo(x.LastName) < 0).ToArray();
 }
 // Task 4
 public static Students[] FindStudentFrom18To24(Students[] listOfStudents)
 {
     return listOfStudents.Where(x => x.Age >= 18 && x.Age <= 24).ToArray();
 }