#include <fstream>

using namespace std;

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

int v[7001], n, x, maxx;

int main()
{
    fin >> n;

    for (int i = 1; i <= n; ++i)
    {
        fin >> x;
        ++v[x];
    }
    for (int i = 1; i < 7000; ++i)
    {
        for (int j = i + 2; j <= 700; j += 2)
            maxx += v[i] * v[j] * v[(i + j) / 2];

        maxx += v[i] * (v[i] - 1) * (v[i] - 2) /2;
    }


    fout << maxx;

    fin.close(); fout.close();
    return 0;
}