#include<stdio.h>
int main(){
	int n;
	scanf("%d", &n);
	int m[1001]; int count = 0;
	for (int i = 0; i < n; i++) {
		scanf("%d", &m[i]);
	}
	int a;
	for (int i = 0; i < n; i++) {
		for (int j = i + 1; j < n; j++) {
			a = m[i] + m[j];
			for (int k = 0; k < n; k++) {
				if (a == m[k])count++;
			}
		}
	}
	printf("%d", count);
	return 0;
}