# include<bits/stdc++.h>
using namespace std;
int n, a[105], s;
int main(){
	cin >> n;
	for(int i = 1; i <= n; i++) cin >> a[i];
	sort(a + 1, a + 1 + n);
	for(int i = 1; i <= n; i++)
		for(int j = i + 1; j <= n - 1; j++){
			if(a[i] + a[j] == a[j + 1] && a[i] != a[j]) s++;
	cout << s;
	return 0;
} 
 求指出错误