/* 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
		Scanner sc=new Scanner(System.in);
		int n=sc.nextInt();
		int a[]=new int[n];
		for(int i=0;i<n;i++)
		a[i]=sc.nextInt();
 
		int k=sc.nextInt();
		int count=0;
		Map<Integer,Integer> hash=new HashMap<>();
		for(int ele:a)
		{
			int cpl=k-ele;
			if(hash.containsKey(cpl))
			count+=hash.get(cpl);
 
			hash.put(ele,hash.getOrDefault(ele,0)+1);
		}
 
		System.out.println(count);
 
 
	}
}

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NQoxIDIgMyAyIDkKNA==

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