#include<stdio.h>
int main()
{
	int i = 0;//数组数的个数
	scanf("%d", &i);
	int arr[100] = { 0 };
	for (int j = 0; j < i; j++)
	{
		scanf("%d", &arr[j]);
	}
	int num = 0;//计数变量
	int a = 0;
	int b = 0;
	int c = 0;
	for (; a < i; a++)
	{
		for (b = a + 1; b < i; b++)
		{
			int ret = arr[a] + arr[b];
			for (c=0; c < i; c++)
			{
				if (ret == arr[c])
					num++;
			}

		}
	}
	printf("%d", num);
	return 0;
}