#include <iostream>
#include <algorithm>
#include <fstream>

using namespace std;

int n, i, j, v[800], st, dr, mid, poz;
long nrt;

int main () {
    
    ifstream fin("nrtri.in");
    ofstream fout("nrtri.out");
    
    fin >> n;
    for (i = 1; i <= n; i++)    fin >> v[i];
    sort (v+1 , v+n+1);
    
    for (i = 1; i <= n-2; i++)
        for (j = i+1; j <= n-1; j++)
        {
            st = j+1;   dr = n;
            while (st <= dr)
            {
                mid = st + (dr-st)/2;
                if (v[mid] <= v[i]+v[j])    {   st = mid+1;   poz = mid;   }
                if (v[mid] > v[i]+v[j])     {   dr = mid-1;   }
            }
            if (st > dr)    nrt += poz-j;
        }
    // 2 3 4 7
    fout << nrt;
}