#include <iostream>
#include <algorithm>
#include <fstream>
using namespace std;

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

const int NMAX = 1000;
int v[NMAX + 1], n;
///obs poz>j


int cautbin(int x)
{
    int p = 1, u = n, poz = -1;
    while(p <= u)
    {
        int m = (p + u) / 2;
        if(x > v[m])
        {
            poz = m;
            p = m + 1;
        }
        else
            u = m - 1;
    }
    return poz;
}

int main()
{
    int nr = 0;
    f >> n;
    for(int i = 1; i <= n; i++)
        f >> v[i];
    sort(v + 1, v + n + 1);
    for(int i = 1; i < n - 1; i++)
        for(int j = i + 1; j < n ; j++)
        {
            ///vom cauta poz=cea mai mare pozitie in v pentru care
            /// v[i]+v[j]>v[poz]
            int poz = cautbin(v[i] + v[j]);
            nr += poz - j; ///cate pozitii avem intre j+1 si poz
        }
    g << nr;
    return 0;
}