#include <iostream>
#include <fstream>
#include <algorithm>

using namespace std;

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

const int DIM = 805;
int n, ans;
int v[DIM];

int cautBin(int l, int r, int x)
{
    int best = -1;
    while (l <= r)
    {
        int m = (l + r) >> 1;
        if (v[m] <= x)
        {
            if (m > best)
                best = m;
            l = m + 1;
        }
        else
            r = m - 1;
    }
    return best;
}

int main()
{
    fin >> n;
    for (int i = 1; i <= n; i++)
        fin >> v[i];
    sort(v + 1, v + n + 1);
    for (int i = 1; i < n; i++)
    {
        for (int j = i + 1; j <= n; j++)
        {
            int x = cautBin(j + 1, n, v[i] + v[j]);
            if (x != -1) ans += x - j;
        }
    }
    fout << ans;
    return 0;
}