var
  fi, fo : text;
  i, j, n, aux, nt, l12, k : longint;
  a : array[1..800] of integer;
begin
	assign(fi,'nrtri.in'); reset(fi);
	assign(fo,'nrtri.out'); rewrite(fo);
  readln(fi,n);
  for i := 1 to n do
  	read(fi,a[i]);
  for i := 1 to n-1 do
  	for j := i+1 to n do
    	if a[i] > a[j] then
      	begin
      		aux := a[i]; a[i] := a[j]; a[j] := aux;
        end;
{  for i := 1 to n-2 do
  	for j := i+1 to n-1 do
    	begin
      	k := j+1; l12 := a[i]+a[j]; // suma lungimilor primelor 2 segmente
        while (l12 >= a[k]) and (k <= n) do
        	begin
        		inc(nt); inc(k)
          end;
      end;}
  write(fo,nt);
  close(fi); close(fo);	
end.