#include <fstream>
#include <algorithm>

using namespace std;

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

int N;
int sol;
int V[1000];

int cb(int lt, int rt, int x)
{
    while (rt - lt > 1)
    {
        int mid = (lt + rt) / 2;

        if (V[mid] <= x)
            lt = mid;
        else
            rt = mid;
    }

    return lt;
}

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 - 1; ++i)
        for (int j = i + 1; j <= N; ++j)
        {
            int sum = V[i] + V[j];
            sol += cb(j, N + 1, sum) - j;
        }

    fout << sol << '\n';

    fin.close();
    fout.close();
    return 0;
}