int main()
{
	int a[20];                                        //????
	int i, cnt;
	i = 0;                                            //???
	cnt = 0;
	cin >> a[i];                                      //????????

	while ( a[i] != -1 )                              //?????????-1.??????
	{
		while ( a[i] != 0 )                           //?????????0??????????0??
		{
			i++;
			cin >> a[i];
		}                                             //?????????i+1??
		for ( int j = 0; j <= i; j++ )                //??????????????????cnt?1
		{
			for ( int k = 0; k <= i; k++ )
			{
				if ( a[k] == 2 * a[j] )
					cnt++;
			}
		}
		cout << cnt - 1 << endl;                      //????????????0?????????0=2*0????
		i = 0;
		cnt = 0;
		cin >> a[i];                                  //????????
	}
	return 0;
}


	