class Record : IComparable<Record>
        {
            public DateTime Date { get; set; }
            public int Num { get; set; }

            #region IComparable<Record> Members

            public int CompareTo(Record other)
            {
                return this.Date.CompareTo(other.Date);
            }

            #endregion
        }

        static void Main(string[] args)
        {
            List<Record> list = new List<Record>();
            list.Add(new Record() { Date = DateTime.Now.AddDays(1), Num = 1 });
            list.Add(new Record() { Date = DateTime.Now.AddDays(2), Num = 2 });
            list.Add(new Record() { Date = DateTime.Now.AddDays(-1), Num = 3 });
            list.Add(new Record() { Date = DateTime.Now.AddDays(-2), Num = 4 });
            list.Add(new Record() { Date = DateTime.Now, Num = 5 });

            DateTime specDate = DateTime.Now;

            Record findOne = list.Where(r => r.Date <= specDate).Max();
            Console.WriteLine(findOne.Num);

            Console.ReadKey();
        }