module Main where

import qualified Data.Vector as V 
import qualified Data.Map as M
import Control.Monad
import qualified Data.ByteString.Char8 as BS

readint :: IO Int
readint = (read . BS.unpack) <$> BS.getLine

readvec :: IO [Int]
readvec = (fmap (read . BS.unpack) . BS.words) <$> BS.getLine

main :: IO()
main = do
  s <- BS.getLine
  let ones = BS.count '1' s
  let zeros = BS.count '0' s
  print $ 2 * min ones zeros
