#include <iostream>
using namespace std;
int main ()
{
    int n;
    cin >>n;
    int a[n+1];
    int zy[22222];
    for (int i=0;i<22222;i++)
    {
        zy[i]=0;
    }
    for (int i=1;i<=n;i++) {int tmp;cin>>tmp;a[i]=tmp;}
    int ct=0;
    for (int i=1;i<=n;i++)
    {
        for (int j=1;j<=n;j++)
        {
            if (j== i ) continue;
            for (int p=1;p<=n;p++)
            {
                if (a[i]+a[j]==a[p] && (zy[i+j]==0))
                {
                    //cout << a[i] <<"+" << a[j] <<"="<<a[p] <<endl;
                    zy[i+j]=1;
                    ct++;
                }
            }
        }
    }
    cout << ct;
    return 0;
}