/* 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
	{
		// your code goes here
		int arr[] = {1,3,4,2,1,2,3};
		int k = 2;
		int n = arr.length;
		int count = 0;
 
		HashMap<Integer,Integer> map = new HashMap<>();
 
		for(int i = 0;i<n;i++){
			int target = k + arr[i];
			if(map.containsKey(target)){
				count = count + map.get(target);
			}
			map.put(arr[i],map.getOrDefault(arr[i],0)+1);
		}
 
		System.out.println(count);
	}
}