import Control.Applicative
import Control.Monad
import Data.List
import Data.Char
import Data.Maybe

main :: IO ()
main = do
    -- 文字列の入力
    sa <- filter (`elem` ['a'..'c']) <$> getLine
    sb <- filter (`elem` ['a'..'c']) <$> getLine
    sc <- filter (`elem` ['a'..'c']) <$> getLine
    -- 出力
    putStrLn $ solve sa sb sc "a"

solve :: String -> String -> String -> String -> String
solve [] _ _ "a" = "A"
solve _ [] _ "b" = "B"
solve _ _ [] "c" = "C"
solve (a:sa) sb sc "a" = solve sa sb sc a
solve sa (b:sb) sc "b" = solve sa sb sc b
solve sa sb (c:sc) "c" = solve sa sb sc c
