If the first sha256 was based on a shorter, less random string, you're far better off attacking that, and then just running sha256 on it. 
But if the first sha256 is of something large or random, then there's no way. Trying to attack it by generating sha256s directly will never work.
But if the first sha256 is of something large or random, then there's no way. Trying to attack it by generating sha256s directly will never work.
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