public class Base
{
public virtual void foo(int x)
{
Console.WriteLine("Base foo(int)");
}
}

public class Derived: Base
{
public void foo(int x)
{
Console.WriteLine("Derived foo(int)");
}
}

class Program
{
static void Main(string[] args)
{
Derived d = new Derived();
int i = 10;
d.foo(i);
}
}