#include<stdio.h>
int main()
{
   int n,i=0,j=0,k=0,l=0; int arr[100] = { 0 };
   scanf_s("%d",&n);
   while (i<n)
   {
   	scanf_s("%d", &arr[i]);
   	i++;
   }
   i = 0;
   while (j < n)
   {
   	k = j + 1;
   	while (k<n)
   	{
   		l = 0;
   		while (l < n)
   		{	
   if (arr[j] + arr[k] == arr[l])
   		i++;
   		l++;
   		}
   		k++;
   	}
   	j++;
   }
   printf("%d", i);
   return 0;
}