#include <fstream>
#include <algorithm>
#include <iostream>
#define N 900
using namespace std;

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

int n, v[N];

int bsearch(int st, int dr, int val)
{
    int m, poz = 0;
    while(st <= dr)
    {
        m = (st + dr) / 2;
        if(v[m] <= val)
        {
            poz = m;
            st = m + 1;
        }
        else if(v[m] > val) dr = m - 1;
    }
    return poz;
}

int main()
{
    int sol = 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 - 2; ++i)
    {
        for(int j = i + 1; j <= n - 1; ++j)
        {
            int x = bsearch(j + 1, n, v[i] + v[j]);
            if( x )
            {
                sol += (x - j);
            }
        }
    }
    g << sol << '\n';
    return 0;
}