Pairs by Difference

using System;
using System.Linq;


namespace PairsbyDifference
{
    class MainClass
    {
        public static void Main(string[] args)
        {
             int[] arr = Console.ReadLine()
                               .Split(' ')
                               .Select(int.Parse)
                               .ToArray();
            int diff = int.Parse(Console.ReadLine());
            int counter = 0;

            for (int i = 0; i < arr.Length ; i++)
            {
                for (int j = i; j < arr.Length; j++)
                {
                    if ( arr[i] != arr[j] &&
                         Math.Abs(arr[i] - arr[j]) == diff )
                    {
                        counter++;
                    }
                }
            }
            Console.WriteLine(counter);
        }
    }
}