#include <bits/stdc++.h>

using namespace std;

ifstream fin("nrtri.in");
ofstream fout("nrtri.out");

int n, v[1000], s;

int cb(int suma, int poz)
{
    int st = poz+1, dr = n, m, last = -1;

    while(st<=dr)
    {
        m = (st+dr) / 2;
        if(v[m] <= suma)
        {
            last = m;
            st = m + 1;
        }
        else
        {
            dr = m - 1;
        }
    }

    if(last!= - 1) return last - poz;
    else return 0;

}

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++)
        {
            s+=cb( v[i]+v[j], j);
        }
    }

    fout<<s;
}