public class Main {

public static void main(String[] args) {
    Scanner scanner = new Scanner(System.in);
    int n = scanner.nextInt();
    int count = 0;
    LinkedList<Integer> arrayList = new LinkedList<>();
    for (int i = 0; i < n; i++) {
        int a = scanner.nextInt();
        arrayList.add(a);
    }

    for (int i = 0; i < n; i++) {
        for (int j = i+1; j < n; j++) {
            if (arrayList.contains(arrayList.get(i) + arrayList.get(j))){
                count++;
            }
        }
    }
    System.out.println(count);
}

}