don't understand

a blonde,brunette,and a red head decided to go on a game show.The object of the game was to walk up 100 stairs without laughing at the joke the host tells you.So te host tells then they're joke then they begin waking.the brunette made it to the 10th step,the red haired girl made it to the 28th step.The blonde made it all the way up to the 100th step then started laughing.Reporters began sorrounding the blonde and asked how did you do that. She answered I just got the joke