#include<iostream>
using namespace std;

int main()
{
	int n;
	cin >> n;
	int a[100];
	for (int i = 0;i < n;i++)
	{
		cin >> a[i];
	}
	int cnt = 0;
	
	int num[20001] = { 0 };

	for (int k = 0;k <= n - 1 - 1;k++)
	{
		for (int i = k+1;i <= n;i++)
		{
			int sum = a[k] + a[i];
			for (int j = 0;j < n;j++)
			{
				if (a[j] == sum)
				{
					num[sum] = sum;
					break;
				}
			}
		}
	}

	for (int i = 1;i <= 20000;i++)
	{
		if (num[i] != 0)
			cnt++;
	}

	cout<<cnt<<endl;

	return 0;
}