"Entering Heaven" joke

A brunette, a redhead, and a blonde were on their way to Heaven. God told them that the stairway to Heaven was 1000 steps, and that on every 5th step he would tell them a joke. He told them not to laugh at any of the jokes along the way or else they would not be able to enter Heaven.

The brunette went first and started laughing on the 45th step, so she could not enter Heaven.

The redhead went next and started laughing on the 200th step, so she could not enter Heaven either.

Then, it was the blonde's turn. When she got to the 999th step, she started laughing.

"Why are you laughing?" God asked. "I didn't tell a joke."

"I know," the blonde replied. "I just got the first joke."