#include <iostream>
#include <fstream>
#include <algorithm>

using namespace std;

ifstream fin("nrtri.in");
ofstream fout("nrtri.out");

int a[800];

int main()
{
    int n,x,y,z,k=0,i;
    fin>>n;
    for(i=1;i<=n;i++)
        fin>>a[i];
    sort(a+1, a+n+1);
    for(x=1;x<n-1;x++)
        for(y=i+1;y<n;y++)
            for(z=y+1;z<n;z++)
                if(a[x]+a[y]==a[z])
                    k++;
    fout<<k<<"\n";
    fin.close();
    fout.close();
    return 0;
}