#include <iostream>
#include <fstream>
using namespace std;
ifstream f("nrtri.in");
ofstream g("nrtri.out");
int v[801],n,i,j,k,nr;
int main()
{
    f>>n;
    for (i=1;i<=n;i++)
     f>>v[i];
    for (i=1;i<=n-2;i++)
     for (j=i+1;j<=n-1;j++)
       for (k=j+1;j<=n;k++)
        if (v[i]+v[j]>=v[k])nr++;
        else break;
      g<<nr;

    f.close();
    g.close();
}