I have an abstract class A and it having virtual method having with partial implementation and it is inherited in class B. I want implement virtual method in derived class, how should i get the base implementation in derived class.
For Example.

```
public abstract class A
{
    public int Sum { set; get; }
    public virtual void add(int a, int b)
    {
        Sum = a + b;
    }
}
class B : A
{
    public override void add(int a, int b)
    {
        // what should i write here
    }
}

```