#include<fstream.h>
ifstream f("nrtri.in");
ofstream g("nrtri.out");
int n,v[801],i,j,ok,k,ko;
int fucmp(const void*a,const void *b)
{ return *((int*)b)-*((int*)a);
}
int main()
{ f>>n;
  for(i=1;i<=n;i++)f>>v[i];
  qsort(v+1,n,sizeof(int),fucmp);
  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&&k-1<=n)ok++;
                                       }
  g<<ok;
  f.close();
  g.close();
  return 0;
}