Переполнение стека при рекурсивной сортировке - C#

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
 
using System.IO;
namespace Sortir_neft
{
    class Program
    {
        static void quicksort(ref int[] a, long l,long r)
        {
            long x = a[(int)Math.Ceiling((double)(l + r) / 2)];
            long i = l;
            long j = r;
            while (i<=j)
            {
                while (a[i]<x)i++;
                while (a[j]>x)j--;
                if (i <= j)
                {
                    int buf = a[i];
                    a[i] = a[j];
                    a[j] = buf;
                    i += 1;
                    j -= 1;
                }
            }
            if (j > 1) quicksort(ref a, l, j);
            if (r > i) quicksort(ref a, i, r);

        }

        static void Main(string[] args)
        {
            string[]s=System.IO.File.ReadAllLines("Input.txt");
          
            int n, i;
            
            n = int.Parse(s[0]);
            int[] nums =s[1].Split(new char[] { ' ', ',' }, StringSplitOptions.RemoveEmptyEntries) .Select(x => int.Parse(x)).ToArray();
      
            StreamWriter fsr = null;
            fsr = new StreamWriter("output.txt");
      
            quicksort(ref nums, 0, n-1);
            foreach (int x in nums)
                fsr.Write(x+" ");

        }
    }
}