import Control.Applicative ((<$>))

main :: IO ()
main = solve <$> map read <$> words <$> getLine >>= print

solve :: [Int] -> Int
solve [a, b, s] | s == 1 = if a == 0 then 2 else a
                | sa <= sb = sa + s
                | otherwise = if a == 0 then sb + s + 1 
                              else sb + min (sa + a) (s - 1 + a)
  where sa = abs (a - s)
        sb = abs (b - s)