//?????????
int main()
{
	int i,j,m=0,count=0;//????
	int num[100];
	for(;;)
	{
		m=0;
		for(i=0;;i++)
		{
			cin>>num[i];//????
			if(num[i]==0||num[i]==-1)//??????????
			{
				count=i;
				break;
			}
		}
		if(num[0]==-1)
			break;
		else
		{
			for(i=0;i<count;i++)//?????????
				for(j=i+1;j<count;j++)
				{
					if((num[i]==2*num[j])||(num[j]==2*num[i]))//?????????
						m++;
				}
				cout<<m<<endl;//????
		}
	}
	return 0;
}