import java.util.*;
public class Main {
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    String s = sc.next();
    int n = s.length();
    int aka = 0;
    int ao = 0;
    
    for(int i = 0 ; i < n ; ++i){
      if(s.charAt(i)=='0'){
        aka++;
      }else{
        ao++;
      }
    }
    
    int ju = Math.min(aka,ao);
    System.out.println(ju*2);
    
  }
}

/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