#include <iostream>
#include <fstream>
#include <algorithm>
using namespace std;
ifstream f("nrtri.in");
ofstream g("nrtri.out");
int v[808],n,s,hi,lo,mi,re;
int main()
{
    f>>n;
    for (int i=1;i<=n;i++)
        f>>v[i];
    sort (v+1,v+1+n);
    for (int i=1;i<=n-2;i++)
        for (int j=i+1;j<=n-1;j++)
        {
            s=v[j]+v[i];
            lo=j;
            hi=n+1;
            while (hi-lo!=1)
            {
                mi=(hi+lo)/2;
                if (v[mi]<=s)
                    lo=mi;
                else hi=mi;
            }
            re=re+lo-j;
        }
    g<<re;
    return 0;
}