import java.util.*;
 
public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String S = sc.next();
        String[] s = S.split("");
        int count0 = 0;
        int count1 = 0;
        for(int i=0; i<s.length; i++) {
            if(s[i].equals("0")) count0++;
            else count1++;
        }
        if(count0 >= count1) System.out.println(count1*2);
        else System.out.println(count0*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