import java.util.*;
public class Main {
   public static void main(String[] args) {  
      Scanner sc = new Scanner(System.in);
      
      String s = sc.nextLine();
      int zero = 0;
      int one = 0;
      for(int i = 0; i < s.length(); i++) {
         if(s.charAt(i) == '0')
            zero++;
         else
            one++;
      }
      System.out.println(2*Math.min(zero, one));
   }
}
/tmp/hf-datasets-cache/medium/datasets/42704881117311-config-parquet-and-info-qiankunmu-Project_CodeNet-896c9d36/hub/datasets--qiankunmu--Project_CodeNet_Python800_and_Java250/snapshots/c899fde44a77ba1cc14973ed3de064e4ff3aadc7/Project_CodeNet_Java250.tar.gz