/*******************************************
 *??????.cpp						   *
 *?????							 	   *
 *????: 2012-10-31			           *
 *??????????????????????*
 *******************************************/


int main(){
	//????a[100][20]???num?????temp???????????????size
	//?????????time?????i,j,k,l
	int a[100][20];
	int num, temp, size, time = 0;
	int i = 0, j = 0, k, l;

	//?????
	while (cin >> num)
	{
		time = 0;		//time?????????????????????
		if (num == -1)	//?num?1?????
			break;

		//??????????0???i??j???????j??1
		else if (num != 0)
		{
			a[i][j] = num;
			j = j + 1;
		}
		//?num?0???????????????
		else if (num == 0)
		{
			size = j;			//?size??
			//??i?????
			for (l = 0; l <  size; l++)
				for (j = 0; j + 1 < size; j++)			//????j + 1 < size??????l = 0?????????????0??
				{
					if (a[i][j] > a[i][j + 1])
					{
						temp = a[i][j];
						a[i][j] = a[i][j + 1];
						a[i][j + 1] = temp;
					}
				}
			//?????????
			for (k = 0; k < size; k++)
				for (l = 0; l < size; l++)
				{
					if (2 * a[i][k] == a[i][l])
						time = time + 1;
				}

			cout << time << endl;	//?????????
			j = 0;					//??????
			i = i + 1;				//??????1?????????

		}
	}

	return 0;
}
