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

using namespace std;
int v[801], n, nrtri, pozitie;
ifstream fin("nrtri.in");
ofstream fout("nrtri.out");

int binarySearch(int st, int dr, int suma)
{
    int mid, ultimul = 0;
    while (st <= dr)
    {
        mid = (st + dr) / 2;
        if (v[mid] <= suma)
        {
            st = mid + 1;
            ultimul = mid;
        }
        else
        {
            dr = mid - 1;
        }
    }
    return ultimul;
}

int main()
{
    fin>>n;
    for(int i=1; i<=n; i++)
    {
        fin>>v[i];
    }
    sort(v+1,v+n+1);
    for(int i=1; i<=n; i++)
    {
        for(int j=i+1; j<=n; j++)
        {
            pozitie=binarySearch(1,n,v[i]+v[j]);
            nrtri+=pozitie-j;
        }
    }
    fout<<nrtri;
    return 0;
}