Gets random number lists to file

randomnumbers.cs

using System;
using System.Collections.Generic;
using System.IO;

namespace cekilis
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("How many numbers you want ?");
            int adet = Convert.ToInt32(Console.ReadLine());
            List<int> items = new List<int>();
            for (int i = 0; i < adet; i++)
            {
                Random r = new Random();
                int s = r.Next(adet);
                if (!items.Contains(s))
                {
                    items.Add(s);
                    Console.WriteLine(items.Count + " : " + s);
                }
                else
                {
                    i--;
                }
            }

            StreamWriter sw = new StreamWriter("numbers.txt",true);
            foreach (int sayi in items)
            {
                sw.WriteLine(sayi);
            }
            sw.Close();
        }
    }
}