Constructor confusion

app.cs

void Main()
{
	var b = new B(1);
}

class A
{
 protected A()
	{
	Console.WriteLine ("A()");
	}
	
	
	public A(int val)
	:this()
	{
		Console.WriteLine ("A({0})", val);
	}

}

class B : A
{
  protected B()
	{
	Console.WriteLine ("B()");
	}
	
public B(int val)
	:base(val)
	{
	Console.WriteLine ("B({0})", val);
	}
	
}

// Define other methods and classes here

output.txt

A()
A(1)
B(1)