import java.util.Scanner;
import java.util.HashSet;
public class Main {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
Scanner in=new Scanner(System.in);
int n=in.nextInt();
int count=0;
int index=0;
int a[]=new int[n];
for(int i=0;i<n;i++)
{
	int m=in.nextInt();
	a[i]=m;
}
 //将重复的数字给去掉
	  HashSet<Integer> hashSet = new HashSet();    
	  for (int i : a)
	  {
	   hashSet.add(i);
	  }
	  int[] b = new int[hashSet.size()];
	  for (int i : hashSet) {
	   b[index++]= i;
	  }



for(int i=0;i<index;i++)
	{
		for(int k=0;k<index;k++)
		{
			for(int m=k+1;m<index;m++)
			{
				if(b[m]+b[k]==b[i])
				{
					count++;
				}
			}
				
					
		}
	}
	
	System.out.print(count);
	
	}

}