#include<iostream>
#include<cstdio>
#include<algorithm>
#include<map>
#include<set>
#include<vector>
#include<cstring>
using namespace std;
int arr[20];
int main() {
    freopen("in.txt","r",stdin);
    int a;
    while(scanf("%d",&a) != EOF && a != -1) {
        memset(arr,0,sizeof(arr));
        arr[0] = a;
        int b,len = 0;
        for(int i = 1; ; i++) {
            cin >> b;
            if(b == 0) break;
            else {
                arr[i] = b;
                len = i+1;
            }
        }
        int ans = 0;
        for(int i = 0; i < len; i++) {
            for(int j = 0; j < len; j++) {
                if(arr[i] == 2*arr[j]) ans++;
            }
        }
        cout << ans << endl;
    }
    return 0;
}