using System;

class Generator {
      public int this[int number] {
         get {
              return Func(number);
         }
      }

      protected virtual int Func(int n) {
          return n;
      }
}

class Square: Generator {   
      protected override int Func(int n) {
          return (n * n);
      }
}

class Fibbonaci : Generator {
      protected override int Func(int n) {
          int res = 0;
          for(int i = 1; n > 0; n--) {
              int j = res;
              res += i;
              i = j;
          }
          return res;
      }
}

class Test {
      public static void Main() {
          Generator Test = new Generator();
          Console.WriteLine("Простой генератор " + Test[5]);
          Test = new Square();
          Console.WriteLine("Квадрат числа 5: " + Test[5]);
          Test = new Fibbonaci();
          Console.WriteLine("10 число Фиббоначи: " + Test[10]);
          if(Test is Generator) Console.WriteLine("Это Generator");
          int c;
          int g = 10;
          f(ref g, out c);
          Console.WriteLine(c);

          Console.ReadLine();
      }
      public static void f(ref int i, out int b) {
          b = i;
      }
}