#include <stdio.h>

int main() {
	int n, m;
	int s, l = 0;
	scanf("%d", &n);
	int a[n];
	for (int i = 0; i < n; i++) {
		scanf("%d", &a[i]);
	}
	for (int i = n - 1; i > 0; i--) {
		for (int j = 0; j < i; j++) {
			if (a[j] > a[j + 1]) {
				m = a[j + 1];
				a[j + 1] = a[j];
				a[j] = m;
			}
		}
	}
	for (int i = n - 1; i >= 0; i--) {
		for (int j = i - 1; j >= 0; j--){
			for (int x = j - 1; x >= 0; x--){
				if (a[i] == a[j] + a[x]) {
					s++;
					l = 1;
					break;
				}
			}
			if (l == 1) {
				break;
			}
		}
	}
	printf("%d", s);
	return 0;
}