#include<fstream.h>
ifstream f("nrtri.in");
ofstream g("nrtri.out");
int n,v[801],i,j,ok,k,ko;
int main()
{ f>>n;
  for(i=1;i<=n;i++)f>>v[i];
  ok=1;
  while(ok) { ok=0;
              for(i=1;i<n-j;i++)if(v[i]<v[i+1]) { ok=v[i];
                                                  v[i]=v[i+1];
                                                  v[i+1]=ok;
                                                  ok=1;
                                                }
              j++;
            }
  for(i=1;i<n-1;i++)for(j=i+1;j<n;j++) { ko=v[i]-v[j];
                                         k=j+1;
                                         while(v[k++]>=ko)ok++;
                                       }
  g<<ok;
  f.close();
  g.close();
  return 0;
}