hacker rank - comparing two lists of numbers (finding the missing numbers in one list)

hacker rank - comparing two lists of numbers (finding the missing numbers in one list)

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

// sample input
// 10
// 203 204 205 206 207 208 203 204 205 206
// 13
// 203 204 204 205 206 207 205 208 203 206 205 206 204

namespace MissingNumbers
{
    class Program
    {
        static void Main(string[] args)
        {
            int firstListCount = int.Parse(Console.ReadLine());
            int[] first = Console.ReadLine().Split(' ').Select(a => int.Parse(a)).ToArray();
            Dictionary<int, int> firstTracks = new Dictionary<int, int>();

            // find each number (in list A), and it's according number of times repeated in the list (use a dictionary for fast access)
            for (int i = 0; i < first.Length; i++)
            {
                if (firstTracks.ContainsKey(first[i]))
                    firstTracks[first[i]]++;
                else
                    firstTracks.Add(first[i], 1);
            }

            // order
            firstTracks = firstTracks.OrderBy(a => a.Key).ToDictionary(a => a.Key, a => a.Value);

            int secondListCount = int.Parse(Console.ReadLine());
            int[] second = Console.ReadLine().Split(' ').Select(a => int.Parse(a)).ToArray();
            Dictionary<int, int> secondTracks = new Dictionary<int, int>();

            // find each number (in list B), and it's according number of times repeated in the list (use a dictionary for fast access)
            for (int i = 0; i < second.Length; i++)
            {
                if (secondTracks.ContainsKey(second[i]))
                    secondTracks[second[i]]++;
                else
                    secondTracks.Add(second[i], 1);
            }

            // order
            secondTracks = secondTracks.OrderBy(a => a.Key).ToDictionary(a => a.Key, a => a.Value);

            // comparing and finding the missing numbers in one of the lists
            foreach (var track in firstTracks)
            {
                if (track.Value < secondTracks[track.Key])
                    Console.Write(track.Key + " ");
            }
        }
    }
}