Crazy Buffet app for iPhone and iPad

David lent quite a lot money to Simon years ago, but Simon never seemed to repay. One day, David found that he didn’t have any cash around to buy any food and he was very starving at that time. He thought to himself , “it’s the time to contact Simon.” Then he went to ask Simon if he could get some money back. As usual, Simon disavowed and said that he didn’t have any cash, but instead, he gave a pile of coupon tickets of his buffet restaurant to David. David swore that he must eat more than what Simon owned him.
Could you help David to eat his money back and revenge?