roman.hs

main = getLine >>= \d -> putStrLn (decToRoman (read d :: Integer)) >> main

decToRoman :: Integer -> String
decToRoman dec
    | dec >= 1000   = "M"   ++ decToRoman(dec - 1000)
    | dec >= 900    = "CM"  ++ decToRoman(dec - 900)
    | dec >= 500    = "D"   ++ decToRoman(dec - 500)
    | dec >= 400    = "CD"  ++ decToRoman(dec - 400)
    | dec >= 100    = "C"   ++ decToRoman(dec - 100)
    | dec >= 90     = "XC"  ++ decToRoman(dec - 90)
    | dec >= 50     = "L"   ++ decToRoman(dec - 50)
    | dec >= 40     = "XL"  ++ decToRoman(dec - 40)
    | dec >= 10     = "X"   ++ decToRoman(dec - 10)
    | dec >= 9      = "IX"  ++ decToRoman(dec - 9)
    | dec >= 5      = "V"   ++ decToRoman(dec - 5)
    | dec >= 4      = "IV"  ++ decToRoman(dec - 4)
    | dec >= 1      = "I"   ++ decToRoman(dec - 1)
    | otherwise     = ""