Appereance Count(not finished)

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

namespace Longest_Increasing_Sequence
{
    class Program
    {
        static void Main(string[] args)
        {
            int lenght = int.Parse(Console.ReadLine());
            var numbersList = new List<int>(lenght);
            for (int i = 0; i < lenght; i++)
            {
                string[] tokens = Console.ReadLine().Split();
                foreach (var token in tokens)
                {
                    int number = int.Parse(token);
                    numbersList.Add(number);
                }
            }
            int checkNumber = int.Parse(Console.ReadLine());
            int [] numbersArr = numbersList.ToArray();
            Array.Sort(numbersArr);
            int counter = 0;
            for (int i = 0; i < numbersArr.Length; i++)
            {

                if (numbersArr.Contains(checkNumber))
                {
                    counter++;
                }
            }
            Console.WriteLine(counter);
        }
    }
}