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

namespace _16.Pair_of_Dffrences
    {
    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;
            int l = 0;
            for (int i = numbers.Length - 1; i > 0; i--, l++)
                {
                for (int k = 0; k < numbers.Length - l - 1; k++)
                    {
                        if ((numbers[i] - numbers[k] == n)| (numbers[k] - numbers[i] == n))
                            {
                            counter++;
                            }
                        }
                    }
            Console.WriteLine(counter);
            }

        }
    }