#include <fstream>

using namespace std;

ifstream f("medie.in");
ofstream g("medie.out");

const int NMAX = 9000,
          VMAX = 7000;

int n, v[NMAX + 1],
    vMax, fr[NMAX + 1];

int main()
{
    f >> n;
    for(int i = 1; i <= n; i++)
    {
        f >> v[i];
        fr[v[i]]++;
        vMax = max(vMax, v[i]);
    }
    long long cnt = 0;
    for(int i = 1; i <= vMax; i++)
        cnt += (long long)fr[i] * (fr[i] - 1) * (fr[i] - 2) / 2;
    for(int k = 1; k <= n; k++)
        for(int j = 1; j < k; j++)
            if(v[j] != v[k] && !((v[j] + v[k]) & 1))
                cnt += (long long)fr[(v[j] + v[k]) >> 1];
    g << cnt;
    f.close();
    g.close();
    return 0;
}