Decreasing random numbers

Hi guys, gotta pretty simple problem that i'm having a headache over. I'm trying to make a Russian roulette game with 1 round and six cylinders. So the behavior to see if pulling the trigger is

[choose random number 1-6]

But how do i make it so that after every shot, the odds are reduced by one?

Create a number attribute and set it's value to a random number between 0 and 6
After you shoot check if the value is greater than 0 and if not decrease the value of that attribute by 1.

I thought it would be something easy like that, thanks!