using System.Collections.Generic;
public static void Main()
var input = new List<DateTime>();
input.Add(DateTime.Today);
input.Add(DateTime.Today.AddMonths(1));
input = input.OrderBy(i => i.Year).ThenBy(i => i.Month).ToList();
DateTime reference = input.First();
foreach (var date in input)
throw new Exception("Cannot have gap months on the priced months.");