C# Online Compiler | .NET Fiddle

using System;
using System.Threading;
					
public class Program
{
	public static void Main()
	{
		
		TwoInstance T1 = new TwoInstance();
		TwoInstance T2 = new TwoInstance();
		TwoInstance T3 = new TwoInstance(); // this will throw an error :) 
	}
	
	public class TwoInstance
	{
	    private static int countInstances=1; 
		//*if you want to get the count outside then make it 
		//public or create a static int method which will return this property*
		
		public TwoInstance()
		{
			Console.WriteLine("Instance" + countInstances + "Created");
			
		    //  countInstances++;    *this is the basic thing which came 
			//  into my mind at the time of iterview but this is not thread safe*
			
			
			Interlocked.Increment(ref countInstances); 
			// thread safe way to increment the counter or we can use LOCK keyword
			if(countInstances>=3)
			{
			 
				throw new Exception("You cannot create more then two object");
			}
			
		}
		
		 ~TwoInstance()
         {
            Interlocked.Decrement(ref countInstances);
         }
	
	}
}

 
using System;
using System.Threading;
                    
public class Program
{
    public static void Main()
    {
        
        TwoInstance T1 = new TwoInstance();
        TwoInstance T2 = new TwoInstance();
        TwoInstance T3 = new TwoInstance(); // this will throw an error :) 
    }
    
    public class TwoInstance
    {
        private static int countInstances=1; 
        //*if you want to get the count outside then make it 
        //public or create a static int method which will return this property*
        
        public TwoInstance()
        {
            Console.WriteLine("Instance" + countInstances + "Created");
            
            //  countInstances++;    *this is the basic thing which came 