Notwithstanding gellyfish's excellent diversion, there is no "longest" way to do it. You can always add another semi-colon.

On the other hand, once you whittle a solution down to the empty string, I'm reasonably sure^* that nothing shorter will show up.

And for the longest contest, after the first few TB solutions, we'll all grow tired of waiting for the latest entry to download.

^* Solutions by TheDamian excepted.