#include <fstream>
#include <algorithm>

using namespace std;

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

int v[802];

int main()
{
    int n, k, ct = 0, x;

    fin >> n;

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

    sort(v, v + n);

    for(int i = 0; i < n - 2; i++) {
        k = v[i] + v[i + 1] + 1;

        x = lower_bound(v + i + 3, v + n, k) - v - 1;

        ct += x - i - 1;
    }

    fout << ct;
    return 0;
}