You have a bunch of three types of coins denominated in dinero. Ashuls are worth 7 dinero each, bindins are worth 5 dinero each, and culkies are worth 11 dinero each.
If you wanted to pay for something exactly in dinero and getting change is not allowed, what is the largest amount in dinero that you can not express with some combination of ashuls, bindins, and culkies?
(For example, 21 dinero can be expressed as 3 ashuls or 2 bindins and 1 culkie, but 8 dinero can not be expressed in terms of the three coin values.)
Submit your answer to Gene Wirchenko <firstname.lastname@example.org>. Your answer should be in the form of a proof. That means to show how your answer must be correct. The deadline is Wednesday, April 19, 2017 at noon Pacific Time. I will post the answer shortly after.