struct A {
       public virtual void foo() {  
          Console.WriteLine("A"); 
       } 
    } 
 
  struct B : A { 
     public virtual override void foo() { 
          Console.WriteLine("B"); 
     }
  } 

 class Program 
 {
    static void Main(string[] args) { 
       A v = new B();
       v.foo(); 
     }  
  }