#include<fstream>
#include<algorithm>

using namespace std;
const int NMAX = 809;
ifstream f ("nrtri.in");
ofstream g ("nrtri.out");
int n,v[NMAX],nrtri;
int main ()
{
    f >> n;
    for (int i = 1; i <= n; ++i)
        f >> v[i];
    sort(v + 1, v + n + 1);
    for (int i = 1; i <= n - 2; ++i)
        for (int j = i + 1; j <= n - 1; ++j)
        {
            int sum = v[i] + v[j];
            int k = j + 1;
            while (sum >= v[k] && k <= n) nrtri++, ++k;
        }
    g << nrtri << '\n';
    g.close ();
    return 0;
}