#include <fstream>

using namespace std;

ifstream f("medie.in");
ofstream g("medie.out");
const int n = 7000;

int fr[n+1],x;
long long ret;


int main()
{
    int m, tmp;
    for ( f >> m ; m; --m)
        f >> x, ++fr[x];
       int i, j;

    for (i = 1; i <= n; ++i)
        for (j = max(1, 2*i-n); j <= min(n, 2*i-1); ++j)
            if (i == j)
            {
                if (fr[i] >= 3)
                    ret += (long long)(fr[i] * (fr[i]-1) * (fr[i]-2));
            }
            else
                ret += (long long)(fr[i] * fr[j] * fr[2*i-j]);
    ret /= 2;
     g << ret;
        return 0;
}