//******************************************
//*?????.cpp                         **
//*??: ??     1100012808              **
//*???2011.10.21                       **
//******************************************
int main()           //???
{            //?????
	int a[16] = {0}, i = 1, j = 1, m = 0, k = 0 ;  //??????
	while (cin >> a[0] )           //???????????
	{                                
	    i = 1; j = 1; m = 0; k = 0 ;    //???????
	    if (a[0] != -1)       //????????????-1??????
	    {
		    do   
			{ 
			    cin >> a[i]; //????????a[0]??????
			    i++;
			}while (a[i-1] != 0);   //???????0??????
		    for (j = 0; j <= i - 2; j++) //??????????????
			{
			    for (k = 0; k <= i - 2; k++)
			    {
			        if (a[j] == 2 * a[k]) //?????????
				    m++;    //????????m?1
		             }
			}                            //???for????
		    cout << m << endl;        
	     }        //???if????
		else break;          // ??????????-1?????
	}            //???while??
	return 0;
}           //?????
			

	    
	



   