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  1. --- Day 4: Ceres Search ---
  2. "Looks like the Chief's not here. Next!" One of The Historians pulls out a device and pushes the only button on it. After a brief flash, you recognize the interior of the Ceres monitoring station!
  3. As the search for the Chief continues, a small Elf who lives on the station tugs on your shirt; she'd like to know if you could help her with her word search (your puzzle input). She only has to find one word: XMAS.
  4. This word search allows words to be horizontal, vertical, diagonal, written backwards, or even overlapping other words. It's a little unusual, though, as you don't merely need to find one instance of XMAS - you need to find all of them. Here are a few ways XMAS might appear, where irrelevant characters have been replaced with .:
  5. ..X...
  6. .SAMX.
  7. .A..A.
  8. XMAS.S
  9. .X....
  10. The actual word search will be full of letters instead. For example:
  11. MMMSXXMASM
  12. MSAMXMSMSA
  13. AMXSXMAAMM
  14. MSAMASMSMX
  15. XMASAMXAMM
  16. XXAMMXXAMA
  17. SMSMSASXSS
  18. SAXAMASAAA
  19. MAMMMXMMMM
  20. MXMXAXMASX
  21. In this word search, XMAS occurs a total of 18 times; here's the same word search again, but where letters not involved in any XMAS have been replaced with .:
  22. ....XXMAS.
  23. .SAMXMS...
  24. ...S..A...
  25. ..A.A.MS.X
  26. XMASAMX.MM
  27. X.....XA.A
  28. S.S.S.S.SS
  29. .A.A.A.A.A
  30. ..M.M.M.MM
  31. .X.X.XMASX
  32. Take a look at the little Elf's word search. How many times does XMAS appear?