2 for 1 Pricing Rule

Hey Ticketing/Pricing Rule Experts,

I need to build a pricing rule where a certain price type can get 2 tickets for the price of 1 for a specific performance. I have not done this before. I am stuck on the best way to do the discount portion of the pricing rule. Has anyone done this before that would be willing to share that portion of their pricing rule? 

Thanks so much!!

Sam