#include<iostream>
#include<vector>
using namespace std;

int main() {
	int n;
	cin >> n;
	vector<int> arr(n);
	for (int i = 0; i < n; i++) {
		cin >> arr[i];
	}
	int t = 0;
	for (int i = 0; i < n; i++) {
		for (int j = 0; j < n; j++) {
			if (j != i) {
				for (int k = j + 1; k < n; k++) {
					if (arr[j] + arr[k] == arr[i]) {
						t++;
						break;
					}
				}
			}
		}
	}
	cout << t;
}