/* 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);
			//this is target sum
	   int sum=sc.nextInt();
		int n=sc.nextInt();
			int arr[]=new int[n];
		for(int i=0;i<n;i++){
			arr[i]=sc.nextInt();
		}
		int count=0;
		HashMap<Integer,Integer>hm=new HashMap<>();
		for(int i=0;i<n;i++){
		int targetValue=sum-arr[i];
		if(hm.containsKey(targetValue)){
			int valueCount=hm.get(targetValue);
			count+=valueCount;
 
		}
		hm.put(arr[i],hm.getOrDefault(arr[i],0)+1);
	}
	System.out.print(count);
}}

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NAo2CjIKNAoyCjMKMgo0

4
6
2
4
2
3
2
4