import java.util.*;
public class Main{
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    String s = sc.next();
    int cnt0 = 0;
    int cnt1 = 0;

    for(int i=0; i<s.length(); i++){
      if( s.charAt(i) == '0')
        ++cnt0;
      else
        ++cnt1;
    }
    int cntMin = Math.min(cnt0, cnt1);
    if(cntMin == 0)
      System.out.println(0);
    else
      System.out.println(cntMin*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