#include <fstream>
#include <algorithm>

using namespace std;

const int L = 9;

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

int cautbin(int v[], int n, int x)
{
    int r = 0, pas = 1 << L;
    while(pas != 0)
    {
        if(r+pas < n && v[r+pas] <= x)
        {
            r += pas;
        }
        pas /= 2;
    }
    return r;
}

int v[801];

int main()
{
    int n, rez = 0, i, j, k;
    in >> n;

    for(i = 0; i < n; i++)
        in >> v[i];
    sort(v, v+n);
    for(i = 0; i < n; i++)
    {
        for(j = i+1; j < n; j++)
        {
            k = cautbin(v, n, v[i]+v[j]);
            if(k>j)
            {
                rez += k-j;
            }
            //out << i << " " << j << " " << k << "\n";
        }
    }
    out << rez;
    return 0;
}