help with codeforces problem 369C

Revision en1, by Gilgamesh_017, 2016-06-26 04:00:28

hello codeforces

can any one please tell me how to solve this problem link,I tried several methods and none of them worked , I also read the tutorial for this problem but it was not clear for me :( thanks

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en2 English Gilgamesh_017 2016-06-26 04:01:15 3
en1 English Gilgamesh_017 2016-06-26 04:00:28 290 Initial revision (published)