#include <fstream>
#include <algorithm>
#define Nmax 805
using namespace std;

ifstream f("nrtri.in");
ofstream g("nrtri.out");

int sum,a[Nmax],n,i,j,h;

int main()
{
   f>>n;
   for (i=1;i<=n;i++)
    f>>a[i];
   sort(a+1,a+n+1);
    for (i=1;i<n-1;i++)
     for (j=i+1;j<n;j++)
    {
        h=j+1;
        while (a[i]+a[j]>=a[h] && h<=n)
         h++;
        sum+=h-j-1;
    }
    g<<sum;
    return 0;
}