C# Derleme Hatası

class deneme {
static void Main(string[] args) {
  string ad, soyad;
  System.Console.Write("adiniz=");
  ad = System.Console.ReadLine();
  System.Console.Write("soyadiniz=");
  soyad = System.Console.ReadLine();
  System.Console.Clear(" adiniz icin f2 cikmak icin esc);
  System.ConsoleKeyInfo KeyInfo = Console.ReadKey(true);
  if (KeyInfo.Key == ConsoleKey.Escape)
  {
   System.Environment.Exit(0);
  }
   else if (KeyInfo.Key == ConsoleKey.F2)
  {
    Console.Write(ad + " " + soyad);
    Console.ReadKey();
}
}

class Deneme {
static void Main(string[] args) {
  System.Console.WriteLine("1.Not : ");
  int not1 = Convert.ToInt32(System.Console.ReadLine());
  System.Console.WriteLine("2.Not : ");
  int not2 = Convert.ToInt32(System.Console.ReadLine());
  ortalama = not1 + not2 / 2;
  System.Console.WriteLine("Ortalama : " + ortalama);
  System.Console.Clear();
  System.Console.ReadKey();
}
}

        static void Main(string[] args)
        {
            string ad, soyad;
            Console.Write("adiniz=");
            ad = Console.ReadLine();
            Console.Write("soyadiniz=");
            soyad = Console.ReadLine();
            Console.Clear();
            Console.Write("adiniz icin f2 cikmak icin esc");
            ConsoleKeyInfo KeyInfo = Console.ReadKey(true);
            if (KeyInfo.Key == ConsoleKey.Escape)
            {
                Environment.Exit(0);
            }
            else if (KeyInfo.Key == ConsoleKey.F2)
            {
                Console.Clear();
                Console.Write(ad + " " + soyad);
                Console.ReadKey();
            }
        }

        static void Main(string[] args)
        {
            Console.WriteLine("1.Not : ");
            int not1 = Convert.ToInt32(Console.ReadLine());
            Console.WriteLine("2.Not : ");
            int not2 = Convert.ToInt32(Console.ReadLine());
            Console.Clear();
            decimal ortalama = (not1 + not2) / 2.0m;
            Console.WriteLine("Ortalama : " + ortalama);
            Console.ReadKey();
        }