import java.util.*;

public class Main {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        String S = sc.next();
        sc.close();
        char S0 = '0';
        int S0mas = 0;
        for(char str : S.toCharArray()){
            if(str == S0){
                ++S0mas;
            }
        }
        int S1mas = S.length() - S0mas;
        if(S0mas < S1mas){
            System.out.println(S0mas * 2);
        }else{
            System.out.println(S1mas * 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