Can You Solve This Mind-Bending Cat Riddle? Count the Legs on the Bus!

I'd like to share an interesting quiz since it is a good riddle, so don't let your mind rest, go ahead and solve this conundrum.

There is a bus with 7 girls. Each girl has 7 bags. In each bag, there are 7 big cats. Each big cat has 7 little cats. Each cat has 4 legs.

Question: How many legs are present on the bus?

Note: The number of legs is the password for the attached file.

Hey, I'm desperate to know the answer. I have tried all possibilities, but somehow flunked in touching the heart of the question. I have got 3-4 answers in my briefcase. Kindly help end my curiosity: is it 406 or 1386, or is it simply 4? What the heck?