/* 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 b[]=new int[n+1];
		
		for(int i=1;i<=n;i++)
		{
			b[i]=sc.nextInt();
		}
		
		Map<Integer,Integer> m=new HashMap<>();
		
		for(int k=3;k<n;k++)
		{
			for(int l=k+1;l<=n;l++)
			{
				int sum=b[k]+b[l];
				m.put(sum,m.getOrDefault(sum,0)+1);
			}
		}
		
		
		int ans=0;
		
		for(int j=2;j<=n-2;j++)
		{
			for(int i=1;i<j;i++)
			{
				int sum=(b[i]+b[j]);
				if(m.containsKey(-sum))
				ans+=m.getOrDefault(-sum,0);
			}
			for(int j1=j+2;j1<=n;j1++)
			{
				int pair=b[j+1]+b[j1];
				m.put(pair,m.getOrDefault(pair,0)-1);
		
			}
		}
		
		System.out.println(ans);
	}
}