Program triunghiuri;
var H : array [1..900] of longint;
    n,i,l,j,m : longint;

procedure swap(var x,y:longint);
     var aux:longint;
      begin
       aux:=x;
       x:=y;
       y:=aux;
      end;

procedure coboara( n, k : longint);
  var fiu : longint;
    begin
         repeat
               fiu:=0;
               if k*2<n then begin
                                  fiu:=k*2;
                                  if H[k*2+1]>H[k*2] then fiu:=k*2+1;
                                  if H[fiu]<=H[k] then fiu:=0
                              end
                        else
               if k*2=n then begin
                                  fiu:=k*2;
                                  if H[fiu]<=H[k] then fiu:=0;
                              end;
               if fiu<>0 then begin
                                    swap(H[k],H[fiu]);
                                    k:=fiu;
                              end;
         until fiu=0;
   end;


procedure heapsort(n : longint);
  var i :longint; begin
     for i:=n downto 2 do  begin
                                swap(H[1],H[i]);
                                coboara(i-1,1);
                           end;
  end;
begin
  assign(input,'HEAPURI.in');reset(input);
  assign(output,'heapuri.out');rewrite(output);
  readln(n); l:=0;
  for i:=1 to n do read(H[i]);
  for i:=n div 2 downto 1 do coboara(n,i);
  heapsort(n);
  for i:=1 to n-2 do
      for j:=i+1 to n-1 do begin
                                 m:=j+1;
                                 while (H[m]<=(H[i]+H[j])) and (m<=n) do
                              begin
                                   l:=l+1;
                                   m:=m+1;
                               end;
                           end;

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