I worked on this problem a while back, I remember I came across this solution in "Challenging Mathematical Problems With Elementary Solutions Vol 1" by Yaglom and Yaglom. I did not understand his solution then and I am no smarter now. I am sorry for not being able to provide more.

I can copy their solution like a chimpanzee would, word for word if you like.

]]>Hi anna_gg;

Thanks. If YOU don't understand it, then I won't even try! Let alone that I have no clue where to find this book

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