#include<bits/stdc++.h>
using namespace std;
int main(){
	int n,a[105],ans=0;
	cin >> n;
	for(int i=0;i<n;i++)cin >> a[i];
	stable_sort(a,a+n);
	for(int i=0;i<n;i++){//±éÀúºÍ
		for(int j=0;j<n;j++){//±éÀúÆäÖÐÒ»¸ö¼ÓÊý
			if(a[i]>a[j]){
				int finds=a[i]-a[j];//ÁíÒ»¸ö¼ÓÊý
				int k=binary_search(a,a+n,finds);//²éÕÒÊÇ·ñ´æÔÚÁíÒ»¸ö¼ÓÊý
				if(k!=-1&&finds!=a[j]){
					ans++;
					break;//·¢ÏÖºóÍ£Ö¹±ÜÃâÖظ´¼ÆËã
				}
			}
		}
	}
	cout << ans;
	return 0;
}