abstract class MyClass
{
  public const int Param1Default = 4;
  public const int Param2Default = 10;

  int Param1 { get; set; }
  int Param2 { get; set; }

  public MyClass(int param1 = Param1Default, int param2 = Param2Default)
  {
    this.Param1 = param1;
    this.Param2 = param2;
  }
}

class Class1 : MyClass
{
  int Param3 { get; set; }
  
  public Class1(int param1 = MyClass.Param1Default, int param2 = MyClass.Param1Default, int param3 = 2)
  : base(param1, param2)
  {
    this.Param3 = param3;
  }
}

public class Test
{
  public static void Main()
  {
    var x = new Class1(7);
  }
}