class Program
    {
        static void Main(string[] args)
        {
            List<int> list = new List<int> { 1, 2, 3, 4, 5 };
            ex<int>(list);
        }
        public static void ex<T>(IList<T> list)
        {
            int? nbr;
            if (list as List<int> != null)
                nbr = (list[0] as int?) + (list[1] as int?);
        }
    }