public static List mostActive(List customers)
        {
            List res = new List();
            foreach (var c in customers)
            {
                double count = customers.Count(a => a.Contains(c));
                double per = (count / customers.Count()) * 100;
                if (!res.Contains(c) && per>=5)
                {
                    res.Add(c);
                }
            }
            return res.OrderBy(r=>r).ToList();
        }