import java.util.*;
public class Main {
  public static void main(String[] args){
    Scanner sc = new Scanner(System.in);
    String S = sc.next();
    int c0 = 0;
    int c1 = 0;
    int len = S.length();
    String NS = S;
    int c = 0;
    for(int i = 0;i < len;i++){
      if(S.charAt(i)=='1'){
        c1++;
      }else{
        c0++;
      }
    }
    c = c1;
    if(c1 > c0)c=c0;
    if(c1==0||c0==0)c=0;
    System.out.println(c*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