Filter c#

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

namespace Filtering
{
    class Program
    {
        public List<string> items = new List<string>();
        static void Main(string[] args)
        {
            Console.Title = "Filter";
            Program c = new Program();
            c.setup();
        }
        public void setup()
        {
            this.write("Type filename to filter\nExample: proxys.txt");
            string filename = Directory.GetCurrentDirectory().ToString() +@"\" +Console.ReadLine(); //we set the name of the file that we want to filter.
            this.filter(filename);
        }
        public void filter(string filename)
        {
            try
            {
                using (StreamReader sr = File.OpenText(filename))
                {
                    string lines = sr.ReadToEnd(); // we read all the lines of the file
                    string[] line = lines.Split('\n'); // we parse all the lanes by new lines.
                    foreach (string filtering in line)
                    {
                        if(!items.Contains(filtering))//we check if our list contains the lane,if not then add it to the list
                        items.Add(filtering);
                    }
                }

                this.write("File has been succesfully filtered");
                string randomfilename = randomString(); // we generate a random filename
                File.Create(randomfilename).Dispose();
                using (TextWriter tw = new StreamWriter(randomfilename))
                {
                    for (int x = 0; x < this.items.Count; x++)
                    {
                        tw.WriteLine(this.items[x]); // we add all the lanes of the list to the new file
                    }
                        tw.Close();
                }
                this.write(string.Format("Everything is done! file has been saved as: {0}", randomfilename));
                Console.ReadLine();

            }
            catch
            {
                this.write(string.Format("Unable to find: {0}",filename));
                Console.ReadLine();
            }
        }
        public void write(string txt)
        {
            Console.WriteLine(string.Format("{0} -- {1}", DateTime.Now, txt));
        }
        public string randomString()
        {
            var chars = "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
            var random = new Random();
            var result = new string(
                Enumerable.Repeat(chars, 8)
                          .Select(s => s[random.Next(s.Length)])
                          .ToArray());
            return result.ToString()+".txt";
        }
    }
}