#include <fstream>
#include <algorithm>
using namespace std;
int v[805], n, i;
void citire ()
{
    ifstream in ("nrtri.in");
    in >> n;
    for (i = 1; i <= n; ++i)
    in >> v[i];
    in.close ();
}
int solve ()
{
    int j, k, nr = 0;
    for (i = 1; i <= n - 2; ++i)
    for (j = i + 1; j <= n - 1; ++j)
    for (k = i + 2; k <= n; ++k)
    if (v[i] + v[j] >= v[k])
    ++nr;
    return nr;
}
void afis (int nr)
{
    ofstream out ("nrtri.out");
    out << nr << '\n';
    out.close ();
}
int main()
{
    citire ();
    afis (solve());
    return 0;
}