#include <iostream>
#include <algorithm>
#include <fstream>
using namespace std;
ifstream in("nrtri.in");
ofstream out("nrtri.out");
int v[100001],n,x,nr;
int main()
{
  in>>n;
  for(int i=1; i<=n; i++)
    in>>v[i];
   sort(v+1, v+n+1);
   for(int i=1; i<=n-1; i++)
    for(int j=i+1; j<=n; j++)
   {
       x=v[i]+v[j];
      int st=j+1, dr=n, mij;
       while(st<=dr)
       {
           mij=(st+dr)/2;
           if(x<v[mij])
           {
               nr++;
               dr=mij-1;
           }
           else st=mij+1;
       }
   }
   out<<nr;
}