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

using namespace std;

int n, v[801], st, dr, mid, nrtri;
ifstream fin("nrtri.in");
ofstream fout("nrtri.out");

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-1; i++)
    {
        for(int j=i+1; j<n; j++)
        {
            st=j+1;
            dr=n;
            while(st<=dr)
            {
                mid=(st+dr)/2;
                if(v[mid] <= v[i] + v[j])
                    st = mid + 1;
                else
                    dr = mid - 1;
            }
            nrtri+=dr-j;
        }
    }
    fout<<nrtri<<'\n';

    return 0;
}