#include <iostream>
#include <fstream>
#include <algorithm>
using namespace std;
ifstream fin ("nrtri.in");
ofstream fout ("nrtri.out");
int t[1000005];
int main()
{
    int i, j, k, ct=0,nrnr,l,r,mij,poz;
    fin >> nrnr;
    for (i=1;i<=nrnr;i++)
    {
        fin >> t[i];
    }
    sort (t+1,t+nrnr+1);
    for (i=1;i<=nrnr;i++)
    {
        for (j=i+1;j<=nrnr;j++)
        {
            poz=j;
            l=j+1;
            r=nrnr;
            while (l<=r)
            {
                mij=(l+r)/2;
                if (t[mij]<=t[i]+t[j])
                {
                    poz=mij;
                    l=mij+1;
                }
                else
                {
                    r=mij-1;
                }
            }
            ct=ct+poz-j;
        }
    }
    fout << ct;



    return 0;
}