//************************************************
//* ??????									
//* ????? 2010 11 8
//* ??????????? 
//***********************************************
int main ()
{
	//????
	int a[16];
	while ((cin >> a[0]) && a[0] != -1 )//???????????????
	{
		int num0 = 1, i, j, k, num=0;
		i = 1;
		while(cin >> a[i] && (a[i] != 0))//???????0
		{
			//?????????
			num0 ++;
			i ++;
		}	
		for(j = 0; j < num0 - 1; j ++)//??n-1?
		{
			for(k = j + 1; k <= ( num0 - 1); k ++)//???????????
			{
				if((a[j] == 2 * a[k]) || (2 * a[j] == a[k]))
				num ++;//???????
			}		
		}		
		cout << num << endl;			
	}
	return 0;
}
