Deserialize String

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

namespace Demo
{
    class Program
    {
        static void Main(string[] args)
        {
            var letterIndices = new SortedDictionary<char, int[]>();

            while (true)
            {
                var line = Console.ReadLine();
                if (line == "end")
                {
                    break;
                }

                var tokens = line.Split(':');
                var letter = tokens[0][0];
                var indices = tokens[1].Split('/').Select(int.Parse).ToArray();

                letterIndices[letter] = indices;
            }

            var flattened = new SortedDictionary<int, char>();
            foreach (var kvp in letterIndices)
            {
                foreach (var index in kvp.Value)
                {
                    flattened[index] = kvp.Key;
                }
            }

            var result = new string(flattened.Values.ToArray());

            Console.WriteLine(result);
        }
    }
}