using System;

​

public class Program

{

    public interface ITest

    {

        void Foo(int x);

    }

​

    class Base : ITest

    {

        public virtual void Foo(int x)

        {

            Console.WriteLine("Base.Foo(int)");

        }

    }

​

    class Derived : Base

    {

        public void Foo(int x)

        {

            Console.WriteLine("Derived.Foo(int)");

        }

​

        public void Foo(object o)

        {

            Console.WriteLine("Derived.Foo(object)");

        }

    }

​

    public static void Main()

    {

        Derived d = new Derived();

        int i = 10;

        d.Foo(i);

    }

}