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Simple. Change it from a Signed INT to an Unsigned INT. That one bit doubles the capacity to 4.2B

I was thinking that they could make an array with 100 spaces in it, with each space storing one digit of the total mesos on a character or being picked up. It takes more lines of code to make, but it also offers more flexibility for the meso limit.

Then again, as Polantaris said, they might be working with 64-bit variables. In which case, my idea is completely unnecessary unless they think they need a tremendous meso cap.