Recently I have learned KMP. I am trying to solve the problem for a while but cant understand, What should be my first approach? Can anyone explain me step by step. Any hint would be greatly appreciated.

Problem Link: http://lightoj.com/volume_showproblem.php?problem=1268 Those Who haven't any Lightoj account dont worry just visit the pdf link then you will see the problem statement. Pdf Link: http://lightoj.com/volume_showproblem.php?problem=1268&language=english&type=pdf

Sorry for my poor English. Thanks a lot.