using System;

using System.Collections.Generic;   

using System.Linq;

public class Program

{

    //do we have duplicates? yes

    //do we want them in our output? no

    //one thing we can do is sort the array and for each unique element smaller than 0 do a binary search and look for its pair - with 0 we can just check wheter there are 2 one next to another

    // this will result in O(nlogn) time complexity

    // another thing is inserting all elements to a hash set and for each element smaller than 0 check if its pair is there as well

    public static void Main()

    {

        var arr = new int[]{0,1,4,0,-1,-4,8,-8,8,-4,2,3,-2};

        var dic = new Dictionary<int,int>();

        foreach(var e in arr){

            if (!dic.ContainsKey(e)){

                dic.Add(e,0);

            }

            dic[e]++;

        }

        foreach(var e in dic.Keys.Where(num => num < 0).ToList()){

            if (dic.ContainsKey(Math.Abs(e))){

                Console.WriteLine(e + "," + Math.Abs(e));

            }

        }

        if (dic.ContainsKey(0) && dic[0] > 1){

            Console.WriteLine("0,0");

        }

    }

}