import java.util.HashMap;
import java.util.Map;
import java.util.Scanner;

public class Main {
    public static void main(String[] args) {
        Scanner in=new Scanner(System.in);
        int n=in.nextInt();
        int ans=0;
        int[] arr=new int[n];
        for (int i=0;i<n;i++){
            arr[i]=in.nextInt();
        }
        Map<Integer,Integer> map=new HashMap<>();
        for (int i=0;i<n;i++){
            for (int j=i+1;j<n;j++){
                map.put(arr[i]+arr[j],arr[i]);
            }
        }
        for (int i=0;i<n;i++){
            if (map.containsKey(arr[i])){
                ans++;
            }
        }
        System.out.println(ans);
    }

}