Pairs_by_Difference

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

namespace _10.Pairs_by_Difference
{
    class Program
    {
        static void Main(string[] args)
        {
            int[] numbers = Console.ReadLine().Split(' ').Select(int.Parse).ToArray();
            int n = int.Parse(Console.ReadLine());
            int counter = 0;

            for (int i = 0; i < numbers.Length; i++)
            {
                for (int k = 0; k < numbers.Length; k++)
                {
                    if (Math.Abs(numbers[k]-numbers[i])==n && i<k)
                    {
                        //Console.WriteLine(numbers[i] + " " + numbers[k]);
                        counter++;
                    }
                }
            }//end of for

            Console.WriteLine(counter);

        }
    }
}