Program triunghiuri;

var V : array [1..900] of longint;
    b1,b2 :array[0..1 shl 17 ] of char;
    n,i,l,j,m : longint;
begin
  assign(input,'nrtri.in'); settextbuf(input,b1); reset(input);
  assign(output,'nrtri.out'); settextbuf(output,b2); rewrite(output);
  readln(n); l:=0;
  for i:=1 to n do read(V[i]);
  for i:=1 to n-2 do
      for j:=i+1 to n-1 do begin
                                 m:=j+1;
                                 while (V[m]<=(V[i]+V[j])) and (m<=n) do
                              begin
                                   l:=l+1;
                                   m:=m+1;
                               end;
                           end;

  writeln(l);
  close(input);
  close(output);
end.