#include <iostream>
#include <fstream>
#include <algorithm>
#define NMAX 800

using namespace std;

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

int n, v[NMAX];

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

    sort(v, v + n);

    long long nrTri = 0;
    int target, st, dr, middle, ans = -1;

    for (int i = 0; i < n - 2; ++i)
        for (int j = i + 1; j < n - 1; ++j) {
            target = v[i] + v[j], st = j + 1, dr = n - 1, ans = -1;
            while (st <= dr) {
                middle = st + ((dr - st) >> 1);
                if (v[middle] > target) dr = middle - 1;
                else {
                    ans = middle;
                    st = middle + 1;
                }
            }
            if (ans != -1) nrTri += ans - j;
        }

    fout << nrTri;
}

/*
7
10 21 22 100 101 200 300
*/