#include<iostream>
using namespace std;
int main(){
int i,j,count,a[20];
cin >> a[0];
while(a[0]!=-1){
int n = 1;
for(;;n++){
cin >> a[n];
if (a[n]==0)
break;
}
count = 0;
for ( i = 0; i < n; i++){
for (j = 0;j < n;j++){
if (a[j]==2*a[i]){
count ++;
break;
}
}
}
cout << count << endl;
cin >> a[0];
}
}