#include<bits/stdc++.h>
using namespace std;
int tub[100010],n,a[1100],s[100010],ans;
int main(){
cin>>n;
for(int i=1;i<=n;i++){cin>>a[i];tub[a[i]]++;}
for(int i=1;i<=n;i++)for(int j=i+1;j<=n;j++)if(tub[a[i]+a[j]]!=0) s[a[i]+a[j]]=1;
for(int i=1;i<=n;i++)if(s[a[i]])ans++;
cout<<ans;
}