#include<iostream>
#include<algorithm>
#include<cstdio>
#include<cstring>
#include<cstdlib>
#include<cmath>
#include<iomanip>
using namespace std;


int a[104];

int main()
{
	int n;
	cin >> n;
	for (int i = 1; i <= n; i++)
	{
		cin >> a[i];
	}
	sort(a + 1, a + n + 1);
	int cnt = 0;
	for (int i = 1; i <= n - 2; i++)
	{
		for (int j = i + 1; j <= n - 1; j++)
		{
			for (int k = j + 1; k <= n; k++)
			{
				if (a[i] + a[j] == a[k])
				{
					ca\nt++;
					break;
				}
			}
		}
	}
	cout << cnt;
	return 0;
}