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

using namespace std;

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

const int MAXN = 810;

int n, sir[MAXN];

int main() {
    fin >> n;

    for (int i = 1; i <= n; ++i)
        fin >> sir[i];

    sort (sir + 1, sir + n + 1);

    int rez = 0;

    for (int i = n; i > 1; --i) {
        int start = 1;
        int end = i - 1;

        while (start < end) {
            if (sir[start] + sir[end] < sir[i])
                ++start;
            else {
                rez += end - start;
                --end;
            }
        }
    }

    fout << rez << "\n";
    return 0;
}