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/Program.cs

using System.Collections.Generic;
					
public class Program
{
	public static void Main()
	{
		var myNewInstance = new KrepselisClass();
		KrepselisClass.KrepselisList.Add(myNewInstance);
		
		// OR
		
		KrepselisClass.KrepselisList.Add(new KrepselisClass());
	}
}

public class KrepselisClass
{
    public static List<KrepselisClass> KrepselisList = new List<KrepselisClass>();
}