Hey Jude weighs in at 7:11, and it was, at the time, the longest song to ever go to number one on the charts. It was also the first song that the Beatles released by themselves on Apple Records. Coincidence? Nope. The lyrics--or the verses, anyway--last just over three minutes, like all pop tunes of the day, but because Hey Jude started out at that slow tempo, it just barely cracks that three-minute barrier.
Conventional wisdom of the day said that if they wanted it to get airplay, they would have to speed it up a bit, to get it in under the wire. Lennon and McCartney, not two lads to have their artistic vision trifled with, told the universe and its conventional wisdom to bugger off and released it themselves on Apple Records, with the song at its original, way-over-3-minutes length. Then, just for a lark, they tacked on the childish playground taunt, "Na na na nana na na", and let it sail up the pop charts. As an aside, you can hear an unedited expletive at about 2:59 on the track; whether this is because of a mistake in the studio or because they were getting a kick out of breaking the 3-minute mark is all conjecture.