var p,q,n,i,j,k,nr,x:longint;
    a:array[1..800] of integer;
    f1,f2:text;
begin
assign(f1,'nrtri.in');
assign(f2,'nrtri.out');
reset(f1);
rewrite(f2);
readln(f1,n);
for i:=1 to n do
 read(f1,a[i]);
for i:=1 to n-1 do
 for j:=i+1 to n do
  if a[i]>a[j] then begin
                     x:=a[i];
                     a[i]:=a[j];
                     a[j]:=x;
                    end;
nr:=0;
for i:=1 to n-2 do
 for j:=i+1 to n-1 do
  begin
   p:=a[i]+a[j];
   q:=j+1;
   while (a[q]<=p) and (q<=n) do
    begin
     nr:=nr+1;
     q:=q+1;
    end;
  end;
writeln(f2,nr);
close(f1);
close(f2);
end.