Suppose you are creating a butterfly spread using call options with 3 different strike prices. Currently, the call price with strike price of $40 is $20.77, the call with strike price of $50 is $12.52, and the call with strike price of $60 is $6.33. What is the initial cash flow of the butterfly spread strategy? If it's a cash inflow, enter a positive number. If it's a cash outflow, enter a negative number.