/***************************
No.1200012819
Name ???
Date 2012-10-31
***************************/


int main()
{
	int a[16] = {0};			//?????16????????????0?
	while (1)				//????????????-1??????
	{
		int i = 0,num = 0,p = 0;  //?????????????????????
		while (1)			//??????????a?????????????0??????
		{
			cin >> a[i];
			if (a[i] <= 0)		//????????????????
				break;
			i++;            //??i???
		}
		if (a[0] == -1)		//??????-1??????
			break;
		for (int j = 0;j < i;j++)  //??a[0]?a[i-1]????????????a[0]?a[i-1]????????
		{
			p = j;                  
			for (int k = 0;k < i;k++)
			{
				if (a[p] * 2 == a[k])//??????nun ?1?
					num++;
			}
		}
		cout << num << endl;
	}
	return 0;
}
