My first thought was that you should either only allow positive numbers or announce that all numbers will be entered as absolute values. The jelly bean game assumes the jar, unseen, may have zero jelly beans, but it won't have a negative quantity. The jar, seen, is presumed to have an undetermined but vaguely bracketable quantity (it more than eight and less than a googol; it's assumed not to have a hidden chamber or a pronounced punt in the base), which helps control the guesses.