> #include <iostream>
> #include <algorithm>
> using namespace std;
> 
> int main()
> {
> 	int i,j,x[20],leight,num;
> 	while(cin>>x[0])
> 	{
> 		if(x[0]==-1)
> 			break;
> 		num=0;
> 		leight=1;
> 		while(cin>>x[leight])
> 		{
> 			if(x[leight]==0)
> 				break;
> 			leight++;
> 		}
> 		sort(x,x+leight+1)；//x【light】是0，不用排序吧？

> 		for(i=0;i<leight;i++)
> 			for(j=i+1;j<=leight;j++)
> 				if(2*x[i]==x[j])
> 					num++;
> 		cout<<num<<endl;
> 	}
> 	return 0;
> }