/*
 * qzlx9.cpp
 *
 *  Created on: 2010-11-17
 *      Author: hanzhe
 */


int main(){                   //????
	int a[16],j;
	while(cin>>a[0]){         //???????
		if(a[0]==-1)break;    //???-1???
		int i=1;
		int l=0;
		while(cin>>a[i]){
			if(a[i]==0)break; //??????0?????
		    for(j=0;j<i;j++)  //??
		    	if((a[i]==2*a[j])||(a[j]==2*a[i]))
		    		l=l+1;
		    i++;
		}
		cout<<l<<endl;
	}
    return 0;
}                              //????
