#include <iostream>
#include <algorithm>
#include <fstream>
using namespace std;
ifstream f("nrtri.in");
ofstream g("nrtri.out");
int main()
{
    int n,v[801],i,a,b,s,nr=0,j,h;
    f>>n;
    for(i=1; i<=n; i++)
        f>>v[i];
    sort(v+1,v+n+1);
    for(i=1; i<n-1; i++)
    {
        a=v[i];
        for(j=i+1, h = i + 2; j<n; j++)
        {
            b=v[j];
            s=a+b;
            //for(h=j+1;h<=n;h++)
            while (h <= n && v[h] <= s)
            {
                nr++;
                h++;
            }
        }
    }
    g<<nr;
    return 0;
}