Help at a problem from Pku judge

Revision en1, by _QWOiNYUIVMPFSBKLiGSMAP_, 2017-11-29 00:27:29

could anyone explai the problem to me and it is solution ? http://poj.org/problem?id=2096

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en1 English _QWOiNYUIVMPFSBKLiGSMAP_ 2017-11-29 00:27:29 130 Initial revision (published)