5 envelopes contain $1000, $2000, $3000, $4000, one remains empty. Then the envelopes are shuffled and in each round you, the player, can either choose to get one of the remaining envelopes or keep the money you have collected so far and quit. If you ask for a new envelope, randomly one of the remaining envelopes is selected and handed to you. If this envelope contains nothing, you lose all the money you accumulated in the previous envelopes, otherwise you add the money to the money taken so far.
You can also change the amount of money in the envelopes. However, envelope number 1 must always contain 0.
Erich Prisner