import Data.List
import Data.Ord
import Data.Char
import Data.Ratio
import Data.Maybe

main = do
  s<-getLine
  putStrLn $maybe "None" (:[]) $lookup False $zip (elemList ['a'..'z'] s) ['a'..'z']

elemList [] _ = []
elemList (x:xs) list  = elem x list : elemList xs list