#include <fstream>
#include <algorithm>
using namespace std;
ifstream f("nrtri.in");
ofstream g("nrtri.out");

int n, s, v[1000], rez;

int main()
{
    int i, j, k;
    f>>n;
    for (i = 1;i <= n;i++)
        f>>v[i];
    sort(v + 1, v + n + 1);
    for (i = 1;i <= n - 2;i++)
    {
        k = 1;
        for (j = i + 1;j <= n - 1;j++)
        {
            s = v[i] + v[j];
            k = max(k, j);
            for (;k <= n && v[k] <= s;k++);
            rez += k - j - 1;
        }
    }
    g<<rez;
}