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diff --git a/Haskell-book/13/Cipher.hs b/Haskell-book/13/Cipher.hs
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+++ b/Haskell-book/13/Cipher.hs
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+module Cipher where
+
+import Data.Char
+import Data.List
+
+vigenere :: String -> String
+vigenere = f (cycle [0, 11, 11, 24])
+    where f _      []       = []
+          f ys     (' ':xs) = ' ' : (f ys xs)
+          f (y:ys) (x:xs)   = (decode (x, y)) : (f ys xs)
+              where decode (x, y) = chr ((mod ((ord x) - 65 + y) 26) + 65)
+
+main :: IO ()
+main = do
+    i <- getLine
+    putStrLn $ vigenere i