using System;

public abstract class MyBase
{
	public abstract bool GetValue(bool value = true);
}

public class MyDerived : MyBase
{
	public override bool GetValue(bool value = false)
	{
		return value;
	}
}

public class Test
{
	public static void Main()
	{
		var derived = new MyDerived();
		Console.WriteLine("Value = {0}", derived.GetValue());
		MyBase myBase = derived;
		Console.WriteLine("Value = {0}", myBase.GetValue());
	}
}