Някъде бъркам с последната проверка и не мога да разбера къде..

Ето и кода...

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace _03.Forum_Topics
{
    class Program
    {
        static void Main()
        {
            var output =new Dictionary<string,HashSet<string>>();

            var input = Console.ReadLine();
            while (input !="filter")
            {
                var outputLine = input.Split(new[] {'-', '>', ','}, StringSplitOptions.RemoveEmptyEntries);
                var topic = outputLine[0];
               
                if (!output.ContainsKey(topic))
                {
                    output[topic]=new HashSet<string>();
                }
                for (int i = 1; i < outputLine.Length; i++)
                {
                    output[topic].Add(outputLine[i]);
                }
               
                input = Console.ReadLine();
            }
            var filter = Console.ReadLine();
            var filterWord = filter.Split(new []{',',' '},StringSplitOptions.RemoveEmptyEntries);

            foreach (var key in output)
            {
                 if (key.Value.Contains(filterWord[0]) || key.Value.Contains(filterWord[1]) )
                  {

                    Console.WriteLine("{0} | #{1}",key.Key, string.Join(", #",key.Value));
                  }
           
            }

        }
    }
}