There is a blonde, a redhead and a brunette on the stairway to heaven.

God says, "There are 3,000 steps and i'll tell you a joke on each 1,000th step you reach. If you laugh you go to hell."

So they start walking and reach to the first 1,000th step. God tells a joke, the brunette laughs and goes to hell.

Then on the 2,000th step God tells a joke, the redhead laughs and goes to hell.

On the 3,000th step God tells a joke, the blonde doesn't laugh and proceeds to the gate.

Suddenly, she bursts out laughing. God asks, "what are you laughing about?", so she replies, "i just got the first joke!".