using System;

using System.Collections.Generic;   

using System.Linq;

public class Program

{

    public static void Main()

    {

        var groups = new List<Group>();

        IEnumerable<string> usersInGroups = groups.Where((group) => true).SelectMany(x => x.members);

        Console.WriteLine(usersInGroups.Count());

    }

    class Group {

        public List<string> members {get;set;}

    }

}