#include <fstream>
#include <vector>
#include <algorithm>
using namespace std;
ifstream fin ("nrtri.in");
ofstream fout ("nrtri.out");
vector<int>v;
int main()
{
  int n,x,nr=0,i;
  fin>>n;
  for(i=1;i<=n;i++)
     {
         fin>>x;
         v.push_back(x);
     }
  sort(v.begin(),v.end());
  vector<int>::iterator it1,it2,it3;
  for(it1=v.begin();it1!=v.end()-2;it1++)
        for(it2=it1+1;it2!=v.end()-1;it2++)
           {
                 it3=upper_bound(it2+1,v.end(),((*it1)+(*it2)));
                 nr=nr+(int)(it3-it2-1);
           }
  fout<<nr;
  fin.close();
  fout.close();
    return 0;
}