500
You are going to visit your grandmother on Mother's day. You want to give her two cakes. However, to get to her house you must cross seven bridges. At each bridge is a troll who demands ½ of all of your cakes as the price to pass. However, these trolls, being a mean trolls, feels spiteful and gives you takes an extra cake.
The puzzle to solve: How many cakes must you leave with to be able to give your grandmother 2 cakes?
504