using System;

public static class ExtensionMethods 

{

    public static void PrintMe(this IModel obj)  

    {       

        Print((dynamic)obj);

    }  

​

    public static void Print(ModelA a)

    {

        Console.WriteLine("A"); 

    }

​

    public static void Print(ModelB b)

    {

        Console.WriteLine("B"); 

    }

}

​

public class Program

{

    public static void Main()

    {

        var a = new ModelA();

        var b = new ModelB();

        a.PrintMe();

        b.PrintMe();

    }   

}

​

public interface IModel

{

}

​

public class ModelA : IModel

{

}

​

public class ModelB : IModel

{

}