Как исправить исключение "System.ArgumentOutOfRangeException"? - C#

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
 
namespace ConsoleApplication3
{
    class Student
    {
        public string FirstName;
        public string LastName;
        public string Group;
        public List<int> Mark = new List<int>();
        public int Year;
        public string Faculty;
        public int CountOf2;
 
    }

    class Program 
    {
        static string probel = "  ";
 
        static List<Student> Base = new List<Student>();
        static List<Student> Base2 = new List<Student>();
        static System.IO.FileStream _File = new System.IO.FileStream("Base.txt", System.IO.FileMode.OpenOrCreate);
        static System.IO.StreamWriter fstr_out = new System.IO.StreamWriter(_File);
 
        static void InStudent()
        {
            Console.Clear();
            Student a = new Student();
            a.CountOf2=0;
            Console.Write("Введите имя : ");
            a.FirstName = Console.ReadLine();
            Console.Write("Введите фамилию : ");
            a.LastName = Console.ReadLine();
            Console.Write("Введите название группы : ");
            a.Group = Console.ReadLine();
            Console.Write("Введите год : ");
            a.Year = Convert.ToInt32(Console.ReadLine());
            Console.Write("Введите факультет : ");
            a.Faculty = Console.ReadLine();
            Base.Add(a);
            
        }
 
        static void OutStudent()
        {
            Console.Clear();
            Student a = new Student();
 
            for (int i = 0; i < Base.Count; i++)
            {
                a = Base[i];
                Console.Write(a.FirstName);
                Console.Write(probel);
                Console.Write(a.LastName);
                Console.Write(probel);
                Console.Write(a.Group);
                Console.Write(probel);
                Console.Write(a.Year);
                Console.Write(probel);
                Console.Write(a.Faculty);
                Console.Write(probel);
                Console.WriteLine();
                
            }
            Console.ReadKey();
        }

        static void OutStudent2()
        {
            Console.Clear();
            Student a = new Student();
 
            for (int i = 0; i < Base2.Count; i++)
            {
                a = Base2[i];
                Console.Write(a.FirstName);
                Console.Write(probel);
                Console.Write(a.LastName);
                Console.Write(probel);
                Console.Write(a.Group);
                Console.Write(probel);
               
                Console.Write(a.Year);
                Console.Write(probel);
                Console.Write(a.Faculty);
                Console.Write(probel);
                 Console.WriteLine();
 
            }
            Console.ReadKey();
        }
      
        static void Menu()
        {
            string b;
            do
            {
                Console.Clear();
                Console.WriteLine("1 – Добавить студента");
                Console.WriteLine("2 – Удалить студента");
                Console.WriteLine("3 – Просмотреть весь список");
                Console.WriteLine("4 - Выход");
                b = Console.ReadLine();
 
                switch (b)
                {
                    case "1": Program.InStudent(); break;
                    case "2":
                        {
                            int index;
                            Console.WriteLine("Введите номер студента, которого Вы хотите удалить (max - {0})", Base.Count);
                            index = Convert.ToInt32(Console.Read());
                            Base.RemoveAt(index);
                        }; break;
                    case "3": OutStudent(); break;
                    case "4": {
                            Console.Clear();
                            for (int i = 0; i < Base.Count; i++)
                                if ((Base[i].CountOf2 >= 2) && (Base[i].Faculty == "КИТ")) 
                                {
                                    Base2.Add(Base[i]);
                                    Base.RemoveAt(i);
                                }
                                else
                                {
 
                                    try
                                    {
                                        fstr_out.Write(Base[i].FirstName);
                                        fstr_out.Write(Base[i].LastName);
                                        fstr_out.Write(Base[i].Group);
                                        fstr_out.Write(Base[i].Year);
                                        fstr_out.Write(Base[i].Faculty);
                                        
                                    }
                                    catch (Exception exc)
                                    {
                                        Console.WriteLine(exc.Message + "Ошибка при работе с файлом.");
                                        return;
                                    }
                                };
                            Console.Clear();
                            Console.WriteLine("Удаленные студенты:");
                            OutStudent2();
                            Console.ReadKey();
 
                                OutStudent();
                          Console.ReadKey();
                              }; break;
                }

            } while (!(b == "5"));
            _File.Close();
            
        }

        static void Main(string[] args)
        {
            Menu();
        }
    }
}