#include <fstream>
#include <vector>

using namespace std;

const int NMAX = 9000;
int v[1 + NMAX];

const int VAL_MAX = 7000;
vector <int> hash_m[1 + VAL_MAX];

int main()
{
    ifstream in("medie.in");
    ofstream out("medie.out");
    int n;
    int nr = 0;

    bool ok;

    in >> n;

    for (int i = 1; i <= n; i++)
    {
        in >> v[i];
        hash_m[v[i]].push_back(i);
    }

    for (int i = 1; i < n; i++)
    {
        for (int j = i + 1; j <= n; j++)
        {
            int mediu = (v[i] + v[j]) / 2;
            for (int k = 0; k < hash_m[mediu].size(); k++)
            {
                if (hash_m[mediu][k] != i && hash_m[mediu][k] != j)
                {
                    nr++;
                }
            }
        }
    }


    out << nr;

    return 0;
}