What is wrong with this encapsulation code

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C#5.0

encapsulation

Hello Friends,
I am not able find out the problem in this code.
My output should be - when i pass the value of Mark as 1 it should return 0 and when i pass as 20 , it should return 20 (via the property 'Mark'). But currently its returning only 0,0 in all cases.
Please help.

class Program
   {
       static void Main(string[] args)
       {
           Encapsulation encapsulate = new Encapsulation();
           encapsulate.Mark = 1;
           encapsulate.Display();
           encapsulate.Mark = 20;
           encapsulate.Display();
           Console.ReadKey();
       }
   }

   public class Encapsulation
   {
       private int _mark;
       public int Mark
       {
           get { return _mark; }
           set
           {
               if (_mark < 5)
                   _mark = 0;
               else
                   _mark = value;
           }
       }

       public void Display()
       {
           Console.WriteLine("Mark: " + Mark);
       }
   }