#include<iostream.h>
void main()
{
	while(1)
	{
		int r1[17],r2[17],k,i=1,j=0,count=0;
		cin>>r1[0];
		if(r1[0]==-1)
			break;
		r2[0]=2*r1[0];
		while (cin>>r1[i]&&r1[i]!=0)
		{
			r2[i]=2*r1[i];
			i++;
		}
		k=i;
		for(i=0;i<k;i++)
			for(j=0;j<k;j++)
				if(r2[j]==r1[i])
					count++;
		cout<<count<<endl;
	}
}