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You have written enough posts to know that you should atleast give some code to show that you've worked out something, but are stuck. Can you show us some code? Programming (and your task) is mostly about teaching the computer what to do - start by enumerating the steps you'd take when executing this task yourself (with primitive abilities that a computer has and not the human sophistication that you possess). Write this all down in your native tongue and the next step is an SMOP :-) Good luck!