//******************************************
//*            ???????              *
//*            ??????                *
//*            ???1200012764            *
//*            ???2012/10/29            *
//******************************************
int main()
{
	int a, t, i;
	while (1)
	{
		a = 0;
		t = 0;
		cin >> a;
		if (a == -1)
		{
			break;
		}
		int num[17] = {0};
		num[1] = a;
		for (i = 2; i <= 16; i++)
		{
			cin >> num[i];
			if (num[i] == 0)
			{
				break;
			}
		}
		for (int r = 1; r <= (i - 1); r++)
		{
			for (int s = 1; s <= (i - 1); s++)
			{
				if (num[r] == 2 * num[s])
				{
					t = t + 1;
				}
			}
		}
			cout << t << endl;
	}
	return 0;
}



