// P2141[NOIP2014 普及组] 珠心算测验
// https://www.luogu.com.cn/problem/P2141

#include <iostream>
#include <cstring>
#include <algorithm>
#include <vector>
#include <cmath>
#include <unordered_map>
#include <unordered_set>
#include <map>
#include <set>
#include <queue>
#include <stack>
#include <deque>
#include <functional>
#include <climits>

#define quickio ios::sync_with_stdio(false),cin.tie(0),cout.tie(0);
#define endl "\n"

using namespace std;
typedef long long ll;

void solve()
{
	int n;
	cin >> n;
	vector<int>v;
	int temp;
	unordered_map<int, int>mp;
	for (int i = 0; i < n; i++)
	{
		cin >> temp;
		v.push_back(temp);
	}
	int sum;
	int ans = 0;
	for (int i = 0; i < n; i++)
	{
		sum = v[i];
		auto it = mp.find(v[i]);
		if (it != mp.end())
			continue;
		else
			mp.insert({ v[i], 0 });
		for (int j = 0; j < n - 1; j++)
		{
			if (j == i)
				continue;
			for (int k = j + 1; k < n; k++)
			{
				if (k == i)
					continue;
				if (v[k] + v[j] == sum)
				{
					ans++;
					break;
				}
			}
		}
	}
	cout << ans << endl;
}

int main()
{
	solve();
	return 0;
}