#include <fstream>
#include <algorithm>
using namespace std;

int limL, limR, n, sol, s, mid, v[801], j;
int main()
{
    ifstream f("nrtri.in");
    ofstream g("nrtri.out");
    f >> n;
    for (int i = 1; i <= n; i++)
        f >> v[i];
    sort (v + 1, v + n + 1);
    for (int i = 1; i <= n - 2; i++)
    for (int j = i + 1; j <= n - 1; j++)
    {
        limL = j;
        limR = n + 1;
        s = v[i] + v[j];
        while (limR - limL != 1)
        {
            mid = limL + (limR - limL)/2;
            if (s >= v[mid]) limL = mid;
                        else limR = mid;
        }
        mid = limL + (limR - limL)/2;
        sol += (mid - j);
    }
    g << sol;
    return 0;
}