I would like to give some feedback about ...
From: https://checkio.org/mission/digit-stack/solve/
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Your result: 13
Your testcase with argument digit_stack(['POP','POP']) gives me result 13
which i failed task.
My local machine with the same code and python version gives me right result -- 0.
Created at: 2016/07/22 19:36; Updated at: 2016/07/22 19:42