import java.io.BufferedReader;
import java.io.*;
import java.util.*;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import java.util.Collections;
import java.util.Arrays;

public class Main {
	public static void main(final String[] args){
    
    final Scanner sc = new Scanner(System.in);
    //final List<Integer> list = new ArrayList<>();
    //final List<Integer> list2 = new ArrayList<>();
    //final List<Long> list3 = new ArrayList<>();

    String s = sc.next();
    int count1 = 0;
    int count2 = 0;

    for(int i = 0; i < s.length(); i++){
        if(s.charAt(i) == '0'){
            count1++;
        }else{
            count2++;
        }
    }

    System.out.println(Math.min(count1, count2)*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