-- ******************************************************************************************
-- * POH6+ (パイザ オンライン ハッカソン)                                                   *
-- * 単語リストの単語を用いて作ることができる最長の回文のうち辞書順(昇順)最小の回文を求める *
-- ******************************************************************************************
 
import Data.List (delete,sort)
 
solve = build "" ""
build r c [] = reverse r ++ c ++ r
build r c (w:ws)
 | reverse w `elem` ws = build (reverse w++r) c next
 | w == reverse w && null c = build r w ws
 | otherwise = build r c ws
 where next = delete (reverse w) ws
 
main = interact $ solve . sort . tail . lines
 

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