#include <iostream>
#include <fstream>
#include <algorithm>
using namespace std;
ifstream fin("nrtri.in");
ofstream fout("nrtri.out");
int n,a[805],i,j,k,nr;
int main()
{
  fin>>n;
  for(i=1;i<=n;i++)
    fin>>a[i];
  sort(a+1,a+n+1);
  for(i=1;i<=n-2;i++)
  {
    for(j=i+1;j<=n-1;j++)
        {
           k=j+1;
          while(a[i]+a[j]>=a[k] && k<=n)
            {
              nr++;
              k++;
            }
        }
  }
  fout<<nr;
    return 0;
}