/* package whatever; // don't place package name! */
 
import java.util.*;
import java.lang.*;
import java.io.*;
 
/* Name of the class has to be "Main" only if the class is public. */
class Ideone
{
	public static void main (String[] args) throws java.lang.Exception
	{
		Scanner sc=new Scanner(System.in);
        int n=sc.nextInt();
        int[] b=new int[n];
        for(int i=0;i<n;i++){
            b[i]=sc.nextInt();
        }
        int k= sc.nextInt();
        int count=0;
        HashMap<Integer,Integer> map=new HashMap<>();
        for(int i=0;i<n;i++){
            int res=k+b[i];
            if(map.containsKey(res)){
                count+=map.get(res);
            }
            map.put(b[i],map.getOrDefault(b[i],0)+1);
        }
        System.out.println(count);
	}
}

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

NQoxIDUgMiA0IDEKMw==

5
1 5 2 4 1
3