#include<bits/stdc++.h>
using namespace std;
int n,cnt;
int main(){
    int a[10005] = {0},b[10005] = {0};
    cin>>n;
    for(int i = 0;i<n;i++){
        cin>>a[i];
        b[i] == 2;
    }
    for(int i = 0;i<n;i++){
        for(int j = i+1;i<n;j++){
            for(int z = 0;z<n;z++){
                if(a[i]+a[j] == a[z]&&b[i] == 2){
                    cnt++;
                    b[i] = 1;
                }
            }
        }
    }
    cout<<cnt;
    return 0;
}