D&D5E - Legendary Actions for Monsters (looking for rules clarification)

I'm a bit confused by the wording of the Legendary Action rules on pg.11 of the D&D5E Monster Manual. As well as the wording of Legendary Actions in some of the Monster Stat Blocks.

MM pg.11
A legendary creature can take a certain number of special actions-called legendary actions-outside its turn. Only one legendary action can be used at a time and only at the end of another creatures turn. A legendary creature regains spent legendary actions at the start of it's turn. It isn't required to use its legendary actions, and it can't use legendary actions while incapacitated.

MM pg.98 - Ancient Red Dragon
The dragon can take 3 legendary actions, choosing from the options below (not included). Only 1 legendary action option can be used at a time and only at the end of another creature's turn. The dragon regains spent legendary actions at the start of it's turn.

So does that mean the Dragon gets to perform a single legendary action over the course of a combat round, as long as it at the end of the turn of another creature. OR, does that mean it can perform up to 3 legendary actions (each at the end of another creatures turn, across the turn endings of multiple creatures) over the course of a combat round.

The former is what my gut wants to be true but the latter is what I think is intended. The latter seems pretty deadly no? Granted these are "Legends" so they should be bad assed. I guess I'm so scarred by 4E's Player over DM Agency the Old School DM is not used to seeing such powerful monsters.

D&D5E - Legendary Actions for Monsters (looking for rules clarification)