DB<1>  @L = 0..27; # use @L rather than @l for more clarity (avoid mistaking 1 and l)

  DB<2>  p $#L;
27
  DB<3> @F = 0..23;

  DB<4> p $#F;
23
  DB<5>  use List::Util 'max';

  DB<6> p max($#L, $#F);
27

##</code><code>##

perl 5, version 14, subversion 4 (v5.14.4)