import java.util.*;
import java.lang.*;
import java.io.*;

class Codechef
{
	public static void main (String[] args) throws java.lang.Exception
	{
	    /*
	        number of unordered quadruplets (i,j,k,l) such that b[i] + b[j] + b[k] + b[l] = 0
	    
	    */
	    
	    
	    //O(n^4) ;
	    Scanner sc = new Scanner(System.in) ; 
	    int n = sc.nextInt() ; 
	    int arr[] = new int[n] ; 
	    
	    for(int i = 0 ; i < n ; i++) {
	        arr[i] = sc.nextInt() ; 
	    }
	    
	    
	    Map<Integer , Integer > map = new HashMap<>() ; 
	    
	    for(int i = 3 ; i < n ; i++) {
	        map.put(arr[i] , map.getOrDefault(arr[i] , 0 ) + 1) ; 
	    }
	    int count = 0 ;
	    for(int i = 0 ; i < n ; i++) {
	        for(int j = i + 1 ; j < n ; j++) {
	            for(int k = j + 1 ; k < n-1 ; k++) {
	                int sum = 0 - (arr[i] + arr[j] + arr[k]) ; 
	                if(map.containsKey(sum)) {
	                    count += map.get(sum) ; 
	                }
	                
	                //remove frequency from map
	                map.put(arr[k+1] , map.get(arr[k+1])-1) ; 
	            }
	            //again updated the frequency ; 
	            for(int k = j + 3 ; k < n ; k++) {
	                map.put(arr[k] , map.getOrDefault(arr[k] , 0) + 1) ; 
	            }
	        }
	    }
	    
	    System.out.println(count);
	}
}