#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];
        
    }
}