/*
 * liangbei.cpp
 *
 *  Created on: 2010-11-12
 *      Author: ??
 */

int main()
{
	int a[20];
	int i;
	int n=0;
	int num=0;
	int j;
	while(1)
	{
		n=0;//??
		num=0;
	    for(i=0;i<20;i++)//??????
	    {
	    	cin>>a[i];
		    if(a[i]==0)//????0???????
		    	break;
		    if(a[i]==-1)//????-1???????
		    	return 0;
		    n++;//?????????
	    }
	    for(i=0;i<n;i++)
	    	for(j=i+1;j<n;j++)
	    		if(a[i]==2*a[j]||2*a[i]==a[j])//???????????????
	    			num++;//???????
	    cout<<num<<endl;
	}
	return 0;

}
