#include <fstream>

using namespace std;

ifstream cin("medie.in");
ofstream cout("medie.out");

const int V_MAX = 14000;

int n;
int x, Mx;
int Sol;

long long F[1 + V_MAX];
long long SP[1 + V_MAX];

int main()
{
    cin >> n;
    for(int i = 1; i <= n; i++)
    {
        cin >> x;
        F[x]++;
        Mx = max(Mx, x);
    }
    Mx *= 2;
    for(int i = 2; i <= Mx; i += 2)
        for(int j = i / 2 - 1; j > 0; j--)
            SP[i] += F[j] * F[i - j];
    Mx /= 2;
    for(int i = 1; i <= Mx; i++)
    {
        Sol += F[i] * SP[i * 2];
        Sol += F[i] * (F[i] - 1) * (F[i] - 2) / 2;
    }
    cout << Sol;
    return 0;
}