#include<iostream>
using namespace std;
int main() {
    int n, q[110], s[100], ans;
    ans = 0;
    cin >> n;
    for (int i = 1; i <= n; i++) cin >> q[i];
    for (int i = 1; i <= n; i++) {
        for (int j = 1; j <= n; j++) {
            for (int k = j + 1; k <= n; k++) {
                if (q[j] + q[k] == q[i] && s[q[i]] != 1) {
                        s[q[i]] = 1; 
                        ans++;
                }
            }
        }
    }
    cout << ans << endl;
    return 0;
}