#include<bits/stdc++.h>
using namespace std;

int main(){
	int n, sum = 0;
	cin >> n;
	int a[n];
	for (int i = 0; i < n; i++){
		cin >> a[i];
	}
	for (int i = 0; i < n; i++){
		for (int j = i+1; j < n; j++){
			if (i == j) continue;
			int ans = a[i]+a[j];
			for (int s = 0; s < n; s++){
				if (s == i || s == j) continue;
				if (a[s] == ans) {sum++;break;}
			}
		}
	}
	cout << sum << endl;
}