#include <bits/stdc++.h>
using namespace std;

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

int v[200001], i, j, n, t;

int main()
{
    in >> n;
    for (i = 0; i < n; i++)
        in >> v[i];
    sort (v, v + n);
    
    int sol = 0;
    for (i = 0; i < n-2; i++)
        for (j = i + 1; j < n-1; j++)
        {
            int suma = v[i] + v[j];
            int st = j + 1, dr = n-1, poz = j;
            
            while (st <= dr)
            {
                int mij = st + (dr - st) / 2;
                if (v[mij] <= suma)
                {
                    poz = mij;
                    st = mij + 1;
                } else dr = mij - 1;
            }
            sol += (poz - j);
        }
    
    out << sol;
	return 0;
}