using System;

using System.Collections.Generic;

using System.Linq;

public class Environment 

{

    public string Id {get; set;}

}

​

public class Program

{

    public static void Main()

    {

        var emptyList = new List<Environment>();

        var list = emptyList.GroupBy(x => x.Id);

        Console.WriteLine(list.Count());

    }

}