#include <iostream>
#include <algorithm>
using namespace std;
int a[103];
int main()
{
	int n; cin >> n;
	for (int i = 1; i <= n; i++)cin >> a[i];
	sort(a + 1, a + n + 1);

	int num = 0;
	for (int i = 1; i <= n; i++)
	{
		for (int j = i+1; j <= n; j++)
		{
			for (int k = j+1; k <= n; k++)
			{
				if (a[i] + a[j] == a[k])num++;
			}
		}
	}

	cout << num;
	return 0;
}