static void Main(string[] args)
        {
            Student s1 = new Student();

            try
            {
                s1.Readdata();
            }
            catch (Myexception ex)
            {
                A.WriteLine("Input for Semester is Inappropriate");
                A.WriteLine("Enter accurate credentials this time\n");
                try
                {
                    s1.Readdata();
                }
                catch (Exception e)
                {
                    A.WriteLine("Inappropriate input");
                    A.WriteLine("Enter accurate credentials this time\n");
                    s1.Readdata();
                }
            }
            catch (FormatException f)
            {
                A.WriteLine("Inappropriate input");
                A.WriteLine("Enter accurate credentials this time\n");
                try
                {
                    s1.Readdata();
                }
                catch (Myexception a)
                {
                    A.WriteLine("Inappropriate input");
                    A.WriteLine("Enter accurate credentials this time\n");
                    s1.Readdata();
                }
            }
            catch (Exception e)
            {
                A.WriteLine("Inappropriate input");
                A.WriteLine("Enter accurate credentials this time\n");
                s1.Readdata();
            }
            finally
            {
                s1.Dispalydata();
            }
        }