#include <fstream>

using namespace std;

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

int n, v[1000], s = 0;

int main()
{
    fin >> n;
    for (int i = 0; i < n; i++)
    {
        fin >> v[i];
    }

    for (int i = 0; i < n; i++)
    {
        for (int j = i + 1; j < n; j++)
        {
            int st = j + 1, dr = n - 1, mij;

            while (st <= dr)
            {
                mij = (st + dr + 1) / 2;

                if (v[mij] < v[i] + v[j])
                {
                    st = mij + 1;
                }
                else if (v[mij - 1] < v[i] + v[j])
                {
                    s += n - mij;
                    break;
                }
                else
                {
                    dr = mij;
                }
            }
        }
    }

    fout << s;

    return 0;
}