using System;
using System.Linq;
using System.Collections.Generic;

public class Test
{
       class Range
        {
            public int? Start { get; set; }
            public int? End { get; set; }
        }

        private static IEnumerable<Range> getAdjacentRanges(IEnumerable<int> nums)
        {
            var ranges = new List<Range>();
            if (!nums.Any())
                return ranges;

            var ordered = nums.OrderBy(i => i);
            int lowest = ordered.First();
            ranges.Add(new Range { Start = lowest });
            int last = lowest;
            Range lastRange = null;

            foreach (int current in ordered)
            {
                lastRange = ranges[ranges.Count - 1];
                if (current > last + 1)
                {
                    lastRange.End = last;
                    ranges.Add(new Range { Start = current });
                }
                last = current;
            }
          
            return ranges;
        }
        
	public static void Main()
	{
	        var arr = new[] { 1, 2, 3, 4, 8, 9, 10, 15 };
            var ranges = getAdjacentRanges(arr)
                .Select(r => r.End.HasValue ? string.Format("{0}-{1}", r.Start, r.End) : r.Start.ToString());
            Console.Write(string.Join(",",ranges.ToArray()));
	}
}