#include <fstream>

using namespace std;

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

int bin(int v[], int val, int n)
{
    int st = 1, dr = n, ans = -1;
    while (st <= dr)
    {
        int med = (st + dr)/2;
        if (v[med] >= val)
        {
            dr = med - 1;
            ans = med;
        }
        else
           st = med + 1;
    }
    return ans;
}
int a[805];
int main()
{
    int n;
    fin >> n;
    for (int i = 1; i <= n; i++)
    {
        fin >> a[i];
    }

    bool sortat = false;
    while (sortat == false)
    {
        sortat = true;
        for (int i = 1; i < n; i++)
        {
            if (a[i] > a[i+1])
            {
                swap (a[i], a[i+1]);
                sortat = false;
            }
        }
    }
    ///sortarea e buna
    int cate = 0;
    for (int i = 1; i <= n; i++)
    {
        ///vrem sa folosim a + b >= c pt un triunghi oarecare
        for (int x = 2; x < n; x++)
        {
            int s = a[i] + a[x+1];
            int poz = bin(a, s, n);
            if (poz > 0)
                cate = cate + (n - poz + 1);
            //fout << a[i] << " " << a[i+1] << " " << poz << " " << cate << endl;
        }
    }
    fout << cate;
    return 0;
}